President Biden on Tuesday reaffirmed his intent to complete the U.S. evacuation mission in Afghanistan by Aug. 31, but he also ordered contingency plans if that cannot be accomplished — a position that stoked a new round of outrage and confusion about the United States’ exit from a two-decade war.

The result was looming uncertainty over whether the United States would finalize its exit within a week, as Biden wants, as well as intensifying anger from would-be Afghan refugees, U.S. allies worried about getting their own personnel out of the country, and veterans concerned about the fate of those who helped the war effort.

Speaking at the White House after meeting virtually with leaders of the Group of Seven large industrialized democracies, Biden said that the United States was on pace to wrap up its efforts in Afghanistan by Aug. 31 and that any extension risked terrorist attacks.

“The sooner we can finish, the better,” Biden said. “Each day of operations brings added risk to our troops.”

But the president also said that meeting that deadline would require avoiding unforeseen disruptions and that it “depends upon the Taliban continuing to cooperate and allow access to the airport for those who we’re transporting out.” He said that he asked the Pentagon and the State Department to draft contingency plans should the U.S. government have to shift its timeline.

Reflecting the moment’s extreme delicacy, CIA Director William J. Burns held a secret meeting Monday in Kabul with the Taliban’s de facto leader, Abdul Ghani Baradar, according to U.S. officials familiar with the matter who spoke on the condition of anonymity to discuss sensitive diplomacy. The White House declined to publicly discuss the decision to dispatch Burns.

The notion of a firm deadline was already drawing sharp criticism Tuesday, even from longtime Biden supporters. “We must extend the withdrawal deadline and work with int’l partners to ensure ALL allies find safety from the Taliban,” tweeted Sen. Jeanne Shaheen (D-N.H.). “Arbitrary deadlines & bureaucracy are no excuse for lives lost.”

The president delivered his remarks on Afghanistan five hours behind schedule and did not take questions from reporters. West Wing officials scrambled to reschedule the day’s events, underlining how the sharply the crisis in Afghanistan has upended the White House’s daily public relations efforts.

Biden’s comments appeared designed to leave some wiggle room amid a volatile situation on the ground in Afghanistan. Yet they did little to quell the frustration of the president’s adversaries and allies, at home and abroad, about his handling of the withdrawal.

The United States has already begun reducing its military footprint at the Kabul airport, the gateway for leaving the country. Pentagon spokesman John Kirby said hundreds of troops had left the airport, but he indicated that a full withdrawal of U.S. troops from the facility has not been ordered. More than 5,000 U.S. troops remain, defense officials said, down from a high of about 5,800.

And evacuations are proceeding apace, Defense Department officials said. Between U.S. military flights and those involving other aircraft, more than 21,000 people were evacuated on Monday alone, Army Maj. Gen. Hank Taylor told reporters at the Pentagon.

The Taliban, which recently ousted the U.S.-backed government in Afghanistan, repeated Tuesday that it views the Aug. 31 deadline as final. The group is still allowing foreign nationals to leave, spokesman Zabiullah Mujahid said, but is barring Afghan nationals from the airport. “We are asking the Americans, please change your policy and don’t encourage Afghans to leave,” he said.

Biden argued that the delicate arrangement that is allowing a steady stream of evacuations will not last forever.

“Thus far, the Taliban have been taking steps to work with us so we can get our people out. But it’s a tenuous situation,” he said. “We’re already had some gunfighting breaking out. We run a serious risk of it breaking down as time goes on.”

Biden heard growing notes of dissent and frustration during a brief virtual meeting with leaders of other major industrialized democracies. All the G-7 nations except Japan also are members of NATO, which fought alongside the United States in Afghanistan for two decades. Several of those leaders favored extending the mission, even briefly, to help evacuate more activists, teachers, prominent women and other vulnerable people.

British Prime Minister Boris Johnson is on record seeking more time. Prime Minister Justin Trudeau on Tuesday said Canada is “ready to stay” in Afghanistan beyond Aug. 31. French President Emmanuel Macron told Biden during a call last week that allies have a “moral responsibility” to extract vulnerable people.

European Union leaders Charles Michel and Ursula von der Leyen pressed Biden on the timeline at the G-7 session on Tuesday. “A lot of leaders, including Ursula and myself, have noted concerns,” Michel said after the meeting. “We’ve got the 31st as a deadline, and we want to know what’s going to happen after that.”

Meanwhile, a group of legislators from G-7 countries discouraged what they called “arbitrary dates for ending military support to the evacuation.” They were joined by Sen. Robert Menendez (D-N.J.), chairman of the Senate Foreign Relations Committee.

Adding their voices were veterans groups, which are focused on Afghan citizens who for years helped American service members as interpreters and in other roles, and who now face possible reprisals from the Taliban.

“If we pull out by August 31st, we are going to leave people who sacrificed their entire lives and their families to protect Americans,” said Jake Harriman, a former Marine Corps officer who has been involved in private efforts to rescue Afghans.

“This excuse that we’re at the whims of the Taliban is insane,” he added.

Paul Rieckhoff, a veterans advocate who served in the Army, voiced similar frustration.

“The level of anger and betrayal being felt across the veterans community right now is off the charts,” he tweeted. Rieckhoff cited an effort launched Monday by dozens of veterans organizations to meet with Biden officials and convey concerns that the United States would pull out before the rescue effort was complete.

In speaking to the G-7 leaders, Biden did not guarantee the mission would wrap up by months’s end, White House press secretary Psaki said, but rather explained that it would finish when the United States had achieved its objectives.

But Psaki was vague about what conditions would trigger the contingency plans Biden has ordered. She said the United States is focused on “evacuating Americans who want to come home, third-country nationals, and Afghans who were our allies during the war.”

U.S. lawmakers also urged the secretaries of state and defense, the chairman of the Joint Chiefs of Staff, and the director of national intelligence to appeal to Biden to reconsider his determination to stick with his timeline. Republicans and Democrats said that if there are still American citizens left in Afghanistan trying to escape, the United States should not adhere to the deadline, regardless of the risk involved in staying.

Sen. Rob Portman (R-Ohio), who has been more willing than many in his party to work with the president this year, issued a statement urging Biden to “rescind the decision to end the evacuation efforts in Kabul on August 31.”

But Biden and his aides stressed that the evacuation process is unfolding with remarkable speed. Taylor said Tuesday that 32 C-17 and five C-130 military aircraft had left Kabul airport in the previous 24 hours, moving 12,700 people out of the country. Coalition and partner aircraft evacuated an additional 8,900 people, for a daily total of 21,600.

The numbers marked a daily record for the evacuation effort, and they came just days before withdrawal operations would have to wind down for the military to meet the Aug. 31 deadline. Since Aug. 14, the United States has evacuated or facilitated the evacuation of more than 70,000 people, according to a White House official.

The number of Americans is far smaller. Defense officials said in a statement Tuesday that about 4,000 “American passport-holders plus their families” had been evacuated. U.S. officials have estimated that 10,000 to 15,000 Americans were in Afghanistan when the Kabul government fell.

“We remain committed to getting any and all Americans that want to leave, to get them out,” Kirby said. “We still believe, certainly now that we have been able to increase the capacity and the flow … that we have the ability to get that done by the end of the month.”

A senior White House official, speaking on the condition of anonymity to describe the president's thinking in advance of his remarks, said the Pentagon recommended that Biden stick to the Aug. 31 deadline. Biden directed the armed forces to continue executing the mission with the expectation of meeting that goal, the official said, but ordered backup plans to be safe.

Patricia Lewis, head of international security research at Chatham House, a London-based think tank, said that if the deadline is to be met, the operation “really needs to wind up pretty soon — in other words, long before the 31st — in order to get all the gear out, all the equipment out, all the people out.”

Questions also mounted Tuesday about the administration’s strategy for future dealings with the Taliban, an oppressive group that Biden has said he does not trust. The Taliban’s decision to prevent Afghan citizens from entering the Kabul airport added to the concern.

“This country needs our doctors, engineers and those who are educated — we need these talents,” said Mujahid, the Taliban spokesman.

Biden said he and the other G-7 leaders had decided to take a unified position when it comes to a Taliban-led Afghanistan.

“We agreed the legitimacy of any future government depends on the approach it now takes to uphold international obligations,” Biden said, including its responsibility to prevent “letting Afghanistan be used as a base for terrorists.”

Reis Thebault, Karla Adam and Karoun Demirjian contributed to this report.