Washington — The U.S. is prepared to quickly lift sanctions on North Korea and promise its leader, Kim Jong Un, that it would not seek to oust him from power, senior officials said Sunday, sketching out the terms of a possible deal if Kim agrees to give up his nuclear weapons.

“We will have to provide security assurances” to Kim as part of a nuclear deal, Secretary of State Mike Pompeo said on Fox News Sunday. “Our hope is that Kim wants a strategic change, and President Trump is prepared to help.”

U.S. officials emphasized that they are not close to finalizing an agreement with Kim, a month before he and President Donald Trump are scheduled to meet in Singapore. They also stressed that Kim would have to agree to broad concessions up front, unlike in previous nuclear deals with Pyongyang that were phased in and ultimately fell apart.

“We’re prepared to open trade and investment as soon as we can,” John Bolton, Trump’s national security adviser, said on ABC’s This Week. Before that can occur, he said, “We want to see the denuclearization process so completely underway that it’s irreversible.”

It remains unclear whether President Trump’s advisers have agreed among themselves on their negotiating goals and how far they are prepared to push North Korea. Bolton appeared to widen the scope of U.S. demands, insisting that the U.S. also wants North Korea to eliminate chemical and biological weapons.

“I think we need to look at their chemical and biological weapons programs,” and the return of South Korean and Japanese citizens abducted by the North, Bolton said.

Pyongyang has long sought assurances the U.S. would not invade the North and is believed to have pursued nuclear weapons in an attempt to ensure the survival of the regime by raising the threat that any U.S. move to oust Kim could escalate into nuclear war.

But it is a matter of debate among diplomats and Korea experts whether Kim would surrender his nuclear arsenal. He has said he is willing to “denuclearize” the Korean peninsula, but it is not clear he means what Washington means — and what concessions he would insist on from the U.S. and its allies.

Pompeo called Kim’s announcement last week that North Korea would destroy its nuclear testing site “a good first step.”

For decades, the U.S. and North Korea have discussed an agreement in which Pyongyang would abandon its nuclear activities in return for a treaty ending the Korean conflict and economic assistance for the impoverished regime. But the negotiations have repeatedly broken down, often with recriminations on each side that the other was not complying with the terms. U.S. government aid to North is not likely, Pompeo and Bolton said.

“Kim understands that this will have to be big and special,” said Pompeo, who returned early Thursday from what he called a “productive” meeting with Kim in Pyongyang. “I think Kim appreciates the fact this is going to have to be different; both sides have to come to play.”

Pompeo implied that the Trump administration would not seek to overthrow Kim if he surrendered his nuclear stockpile.