Speaking at the site where an airliner ripped into the Pentagon 18 years ago, President Trump said Wednesday that the United States is hitting “our enemy harder than they have ever hit before,” days after he called off negotiations aimed at winding down the war in Afghanistan.

The claim brought some applause during a memorial marking the anniversary of the Sept. 11, 2001, terrorist attacks, but also skepticism. The number of U.S. troops in Afghanistan is just over 10 percent of what it was at the height of the war.

The comment also underscored a fundamental issue for the military and the Trump administration: Although the president has pledged to end America’s “endless wars,” there are no easy solutions in sight.

“As each year passes and the details of that tragic day fade, we must ensure the memories of the departed do not,” said Defense Secretary Mark T. Esper. “This memorial where we gather for today’s ceremony stands as an enduring testament to remember them, to honor them, to recall their sacrifice. But also, it inspires future generations to serve in defense of our great nation.”

The war in Afghanistan began after the Taliban government provided refuge to al-Qaeda leader Osama bin Laden and his cohorts before the 9/11 attacks. It has meandered for years, even after a Navy SEAL team killed bin Laden during a raid in neighboring Pakistan in May 2011.

On Wednesday, the top U.S. commander in Afghanistan, Army Gen. Austin “Scott” Miller, spoke at a closed memorial service at the headquarters of the U.S.-led military coalition. The ceremony commemorated not only those lost on Sept. 11, but also the thousands of U.S., Afghan and other coalition service members who have died in the war since, said Army Col. Sonny Leggett, a U.S. military spokesman in Kabul.

Clashes between U.S. and Afghan forces and the Taliban have increased across the country, a defense official familiar with the ongoing operations said. The official, speaking on the condition of anonymity because of the sensitivity of the situation, attributed the fighting to “jockeying” ahead of Afghan presidential elections scheduled for Sept. 28, an increase in violence as Afghanistan’s traditional fighting season comes to a close and uncertainties created by the abrupt end of negotiations between the Trump administration and Taliban officials on Saturday.

U.S. defense officials have declined repeatedly to address what could come next for the military in Afghanistan. The negotiations called for the Pentagon to withdraw about 5,400 of the 14,000 U.S. troops deployed, and it is not clear whether Trump will still pursue that level without a deal with the Taliban.

Over the weekend, Secretary of State Mike Pompeo said American forces had killed roughly 1,000 Taliban fighters in the previous 10 days. The statement echoed controversial body counts the United States used as a metric for success during the Vietnam War even as security there crumbled, but the defense official familiar with U.S. operations in Afghanistan said it is accurate.

The Taliban, he said, “are taking some really heavy casualties.”

U.S. officials released data showing that the military launched 810 strikes in August. Overall for the year, Air Force data shows the United States is on track to drop about the same number of munitions as in 2018.

Whatever the situation surrounding the pace of U.S. operations, Pentagon leaders have acknowledged for years that the conflict is stuck in a bloody stalemate, and much of the countryside remains under partial or full Taliban control.

Johnny Walsh, a former diplomat who worked on Afghanistan peace issues and is now at the U.S. Institute of Peace, said Taliban fighters are motivated by two primary goals: to end what they characterize as a foreign military occupation and to defeat what they see as a government dominated by foreign influence.

Their nationalist message “allows them to recruit a basically endless supply of new fighters from every corner of the country,” he said. Although a majority of Afghans oppose the Taliban, the militant group “has been very effective in tapping into the sector of society who support them.”

David Barno, a retired three-star general who commanded American forces early in the war, described the Taliban as a resilient and “deeply rooted” organization. Even the kind of Special Operations raids that intensified during the peak of U.S. combat operations were likely to have only a transient impact on the group’s strength, Barno said, as new insurgent leaders replace those killed.

“That’s the issue with ‘mowing the grass,’ ” he said.

The U.S. military continues to carry out counterterrorism operations in numerous countries, including Iraq, where victory was declared over the Islamic State in March. On Tuesday, U.S. military officials released video of American fighter jets dropping some 80,000 pounds of bombs on an island in the Tigris River “infested” with Islamic State fighters.

In Washington, former president George W. Bush and his defense secretary as the wars were launched, Donald H. Rumsfeld, visited the black stone of the Pentagon Memorial in a separate, small event after Trump left.

Bush hung a white floral wreath at the memorial and visited with a small group of people waiting to meet with him, including first responders. He made no public remarks but shook hands with several people and embraced one woman, Lisa Dolan of Alexandria, after she approached him. Her husband, Navy Capt. Robert Dolan, was killed when American Airlines Flight 77 crashed into the Pentagon.