Secretary of State Rex Tillerson said Monday that North Korea could show it is ready for negotiations by stopping missile launches, and said he told Russian diplomats that the Kremlin’s meddling in U.S. elections had created “serious mistrust” of them among Americans.

North Korea, meanwhile, reacted to the U.N. Security Council’s new sanctions by threatening a “thousands-fold” retaliation against the United States and asserting that sanctions would never force the country to abandon its nuclear program. “There is no bigger mistake than the United States believing that its land is safe across the ocean,” according to the government statement carried by the official media.

Yet in his remarks to reporters at a regional conference in which North Korea’s missile and nuclear tests have dominated discussions, Tillerson held out an olive branch to Pyongyang by saying the United States will sit down for talks “when conditions are right” to discuss denuclearization and steps to ensure North Korea can feel secure and prosperous.

“The best signal that North Korea could give us that they’re prepared to talk would be to stop these missile launches,” he said. “We’ve not had any extended period of time where they have not taken some type of provocative action by launching ballistic missiles. I think that would be the first and strongest signal they could send to us, would be to stop these missile launches.”

Pressed for a time frame, Tillerson said, “We’ll know it when we see it.”

“We’re not going to give someone a specific number of days or weeks,” he added. “This is not ‘Give me 30 days and we’re ready to talk.’ It’s not quite that simple. It is all about how we see their attitude in approaching a dialogue with us.”

Tillerson has used the Association of Southeast Asian Nations (ASEAN) gathering here in the Philippine capital to hold meetings on the sidelines with allies and adversaries.

Following a meeting with his counterparts from Australia and Japan, the three countries issued a statement urging the international community to pressure North Korea to abandon its “threatening and provocative” actions, urging the new sanctions be strictly implemented.

Tillerson also said that when he met with Russian Foreign Minister Sergei Lavrov on Sunday, he tried to drive home the point that Russia’s meddling in the 2016 presidential election had a deep and divisive effect on relations between the two countries.

He described his conversation with Lavrov as “trying to help them understand just how serious this incident had been and how seriously it had damaged the relationship between the U.S. and the American people and the Russian people — that this had created serious mistrust between our two countries and that we simply have to find some way to deal with that.”

Tillerson said he also told Lavrov the United States has still not decided how to respond to Russia’s move to expel hundreds of U.S. diplomats. He said a response would come by Sept. 1.

Earlier Sunday, China delivered frank advice to North Korea, its outcast neighbor, telling Pyongyang to make a “smart decision” and stop conducting missile launches and nuclear tests.

The statement by Chinese Foreign Minister Wang Yi came on the heels of a U.N. Security Council decision to impose additional sanctions on North Korea and its exports, and it suggested that the American push to further isolate the regime of Kim Jong Un is reaping some dividends. But Wang also called on the United States to dial back the tension.

After meeting with North Korea’s top diplomat at the ASEAN gathering here, Wang said that the situation on the Korean Peninsula is critical — but that it could be a turning point for negotiations over North Korea’s nuclear proliferation.

“Do not violate the U.N.’s decision or provoke international ­society’s goodwill by conducting missile launching or nuclear tests,” Wang said after talks with Ri Yong Ho, North Korea’s foreign minister. Wang, however, quickly added, “Of course, we would like to urge other parties like the U.S. and South Korea to stop increasing tensions.”

Tillerson arrived in Manila on Saturday night in what State Department officials said would be a concerted effort to enlist other countries in the campaign to get North Korea to abandon its missile and nuclear tests. Concern has mounted that North Korea is developing its missile technology more quickly than expected, after tests last month of missiles that experts said are capable of striking the U.S. mainland, perhaps as far inland as Chicago.

“Certainly we want to resolve this issue through negotiations, and this pressure campaign, the sanctions, it’s all about trying to convince the North Koreans that the fast way forward is to come back to the table and talk,” said Susan Thornton, assistant secretary for East Asian and Pacific affairs.

President Trump, who is at his golf club in New Jersey, tweeted on Sunday night: “Just completed call with President Moon of South Korea. Very happy and impressed with 15-0 United Nations vote on North Korea sanctions.”

In the hour-long phone call, Trump and South Korean President Moon Jae-in agreed to cooperate and apply maximum pressure and sanctions on North Korea in a telephone call on Monday, the South’s presidential office said, according to Reuters.

Moon was quoted as saying there is a need to show North Korea that the door to dialogue is still open, should Pyongyang give up its nuclear program.

In Washington, White House counselor Kellyanne Conway reveled in the vote, which took place Saturday. On ABC’s “This Week,” she said Sunday: “And then you also just yesterday saw a unanimous rebuke of North Korea. The greatest economic sanctions package ever levied against them, it’ll cost about $1 billion. Even allies in the region like China, Japan, South Korea, all agreeing with the United States that North Korea and its nuclear capabilities must be stopped.”

But Tillerson also has pointedly stated several times that the United States does not seek regime change or a rapid reunification of the Koreas, which have been in a state of suspended hostility since an armistice was declared in 1953.

On Sunday, he declared the latest U.N. sanctions a “good outcome.” That prompted South Korean Foreign Minister Kang Kyung-wha to correct him slightly. “It was a very, very good outcome,” she said.

South Korean officials told reporters that Kang and Tillerson had agreed to pursue the denuclearization of the Korean Peninsula through peaceful measures.

But the diplomatic road ahead is rocky. U.S. officials rejected Beijing’s call for the North to halt its nuclear program in exchange for the United States and South Korea suspending joint military exercises, which Pyongyang considers a prelude to an invasion and regime change.

“This kind of moral equivalency that’s implied by the freeze for freeze, which is between the North Koreans shooting off missiles that are prohibited and our reasonably defensive exercises that we undertake in our alliance with the South Koreans to protect them from these launches, is not a reasonable kind of a trade,” Thornton said.

Thornton also said the United States would be “watchful” to ensure that China did not slip from its adherence to the new sanctions, which she characterized as the strongest in a generation.

“We want to make sure China is continuing to implement fully the sanctions regime,” she said. “Not this kind of episodic back and forth that we’ve seen.”

The United States has unsuccessfully lobbied for the 27 members of the ASEAN Regional Forum to suspend North Korea’s membership. The response has been polite but noncommittal.

U.S. officials have been adamant that there will be no direct meetings with North Koreans in Manila, even among lower-level officials.

The ASEAN conference also addressed other issues of regional concern.

Delegates are working to establish the framework for a code of conduct in the South China Sea that would reaffirm respect for the freedom of navigation and overflight, and outline how to arbitrate disputes. The demands that China stop expanding and reinforcing man-made islands in the sea, however, have been watered down from a year ago as more pressing demands have risen to the forefront.

The United States is particularly concerned about Islamist militants gaining a foothold in the Philippines after being pushed out of Syria and Iraq. In the city of Marawi in the country’s south, Philippine forces are fighting militants who claim to be affiliated with the Islamic State.

Tillerson started the day on a somber note when he visited the Manila American Cemetery and Memorial, where 17,000 American and Philippine troops who fought in the Pacific during World War II are buried.

After touring the site and walking past large stone slabs inscribed with the names of more than 36,000 men and women missing in action in the theater between 1941 and 1945, Tillerson signed a visitors’ book, adding after his signature, “Let us never forget — FREEDOM.”