SINGAPORE — The U.S. is demanding the complete and verifiable nuclear disarmament of North Korea — but is willing to offer "unique" security assurances in return, Secretary of State Mike Pompeo said Monday.

He was talking hours before an unprecedented face-to-face meeting between President Donald Trump and North Korean leader Kim Jong Un in Singapore.

"We are prepared to take actions that will provide [North Korea] sufficient certainty that they can be comfortable denuclearization isn't something that ends badly for them," Pompeo said at a news conference. "Indeed just the opposite, that it leads to a brighter, better future for the North Korean people."

The talks between U.S. and North Korean officials have "moved more quickly than expected," the White House said in a statement released a little after 8 p.m. local time Monday.

The White House said Trump plans to meet with Kim in four settings Tuesday: an official greeting, a one-on-one session (with translators), as part of an expanded bilateral group and then at a working lunch. He'll give a press conference before departing Singapore for Washington earlier than expected — about 8 p.m. local time Tuesday night — the White House said.

Despite the optimistic tone of the White House press office, Pompeo would not go into detail about what the U.S. might offer in return for Kim giving up his arsenal of nuclear weapons.

"We're prepared to give security assurances that are different, unique to what America has been willing to provide previously," he said. "We think this both necessary and appropriate."

He said any economic relief would not be provided until the U.S. had proof that its demands had been met.

"The ultimate objective we seek from diplomacy with North Korea has not changed," he told reporters. "The complete, verifiable and irreversible denuclearization of the Korean Peninsula is the only outcome that the United States will accept."

Pompeo also appeared to manage expectations in terms of the initial discussions, which will open with the sit-down between Trump and Kim itself.

"These discussions ... will set the framework for the hard work that will follow," he said. "We'll see how far we can get, but I'm very optimistic that we will have a successful outcome."

Pompeo also revealed that Trump had spoken with Japanese Prime Minister Shinzo Abe and South Korean President Moon Jae-in earlier Monday.

He said 5,000 reporters would be covering the summit in Singapore.

"President Trump is going into this meeting with confidence, a positive attitude and eagerness for real progress," Pompeo added. "He has made it clear that if Kim Jong Un denuclearizes there is a brighter future for North Korea. Tomorrow, we will get our clearest indication to date whether Chairman Kim Jong Un shares this vision."