Secretary of State Rex Tillerson called Tuesday for a dialogue with North Korea and acknowledged that U.S. relations with Russia have worsened during the Trump administration.

During wide-ranging comments at the State Department marking six months since his confirmation, Tillerson told reporters that the United States does not aim to depose the government in Pyongyang or use military force.

“We do not seek a regime change, we do not seek a collapse of the regime, we do not seek an accelerated reunification of the peninsula, we do not seek an excuse to send our military north of the 38th Parallel,” he said.

“We are trying to convey to the North Koreans: ‘We are not your enemy, we are not your threat. But you are presenting an unacceptable threat to us, and we have to respond.’ ”

Tillerson added that the United States hopes that “at some point,” North Korea will understand and sit down for a dialogue.

The secretary of state said the administration has been attempting to exert “peaceful pressure” on North Korea, “because the options available to us are limited, particularly if we think we are operating under a short period of time.”

Tillerson talked to reporters during a surprise appearance in the briefing room, his first since becoming secretary six months ago. He expressed concern about Iran’s regional ambitions, unrest in Venezuela and war in Ukraine. He also said he has a “good” relationship with President Trump, who calls him daily, including late at night and on weekends, “when something comes to his head.”

Tillerson said that despite the United States’ deteriorating relationship with Russia, the countries still can cooperate on Syria and counterterrorism, items that will be on the agenda when Tillerson meets Russian Foreign Minister Sergey Lavrov this weekend at a summit in the Philippines.

“I don’t think the American people want us to have a bad relationship with a huge nuclear power, but I think they are frustrated,” he said.

Tillerson quoted Trump telling Lavrov, “We need some good news with Russia,” when they met in the Oval Office. Tillerson said he has warned Russian President Vladimir Putin and Lavrov that “the situation’s bad, but believe me, it can get worse. And it just did.”

Putin’s decision to slash the staff at the U.S. Embassy in Moscow, Tillerson suggested, was a play to domestic politics after Barack Obama expelled Russian diplomats and seized two Russian properties in the closing weeks of his presidency.

“He felt he had to do something,” Tillerson said of Putin. “Does it make our life more difficult? Of course it makes our life more difficult.”

Tillerson voiced skepticism about whether the nuclear deal with Iran, officially known as the Joint Comprehensive Plan of Action, has value for the United States.

“It’s an agreement that should serve America’s interests first and foremost, and if it doesn’t serve that interest, then why would we maintain it?” Tillerson said.

Iran was supposed to “become a good neighbor,” but instead has continued its ballistic missile program, he said.

“The spirit of the agreement has been violated,” Tillerson said, adding that that view is shared among the European countries that were also parties to the agreement.

“Do we want to tear it up and walk away?” he said. “Do we want to make the point to Iran that we expect you to get back in line with the spirit of the agreement, and we’re going to stay here and hold you accountable to it?”

Tillerson has argued that the deal is flawed but should be maintained, at least for now, because the alternative is worse.

“I think there are a lot of alternative means with which we use the agreement to advance our policies in the relationship with Iran,” he said. “And that’s what the conversation is around, generally, with the president, is what are all those options.”

Tillerson also expressed alarm about Venezuela, and suggested that the United States would be pleased if President Nicolás Maduro decided to leave office.

“The situation from a humanitarian standpoint is already becoming dire,” Tillerson said.

He brushed off the criticism of his management of the State Department. Hundreds of senior positions are unfilled, and some of his positions have been rebutted by the White House or a presidential tweet. The criticisms have fed rumors that he is frustrated about sparring with the White House over policy and complaints within the department he is trying to “redesign” for the 21st century, and that has considered resigning. But Tillerson sounded resolute Tuesday, describing his relationship with Trump as “very open.”

“It’s one in which I feel quite comfortable telling him my views,” he said. “He and I have differences of views on things like [the Iran nuclear deal] and how we should use it. I think if we’re not having those differences, I’m not sure I’m serving him.”