US President Donald Trump has said there is a "substantial chance" a historic summit with North Korea's Kim Jong-un next month may be delayed.
He was speaking as he received South Korea's President Moon Jae-in at the White House to discuss the summit.
Moon is "likely tell President Trump what to expect and what not to expect from Kim", South Korean media report.
Last week the North said it might cancel if the US insisted on it giving up nuclear weapons unilaterally.
The 12 June summit is due to take place in Singapore. It follows a summit between Kim and Moon in April.
"If it does not happen, maybe it will happen later," Trump was quoted as saying by AFP news agency at the start of his talks with Moon.
North Korea is expected to dismantle a nuclear test site this week as a good will gesture but the demolition may be delayed by bad weather.
How did the mood sour last week?
North Korea cancelled high-level talks with South Korea, saying the South's joint military exercises with the US were a "provocation" and rehearsal for invasion.
Pyongyang then accused US national security adviser John Bolton of making "reckless statements" after he suggested the North could follow a "Libya model" of denuclearisation.
That was a reference to Libya's former leader, Muammar Gaddafi, who agreed to give up nuclear weapons in 2003 and was later killed by Western-backed rebels.
Trump, however, later denied the US would follow the "Libyan model" if an agreement was reached with North Korea.
"The model, if you look at that model with Gaddafi, that was a total decimation," he said.
"We went in there to beat him. Now, that model would take place if we don't make a deal, most likely. But if we make a deal, I think Kim Jong-un is going to be very, very happy."
Why does the Singapore summit matter so much?
Trump accepted North Korea's invitation for direct talks after more than a year of heated rhetoric between Washington and Pyongyang, amid global concern hostility might escalate into military confrontation.
The New York Times reported on Sunday that Trump was asking aides and advisers whether he should proceed with the Kim summit.
North Korea conducted several nuclear tests over the past few years and developed long-distance missiles which, it says, can carry nuclear bombs as far as the US mainland.
If the summit happens, it would be historic as no sitting US president has ever met a North Korean leader.
Even then, is a deal likely?
Many observers believe the two leaders now have too much at stake for the summit not to go ahead.
However, Pyongyang's professed commitment to "denuclearisation" is likely to differ from Washington's demand for "comprehensive, verifiable and irreversible" nuclear disarmament.
North Korea has said it will start dismantling its nuclear test site this week, in a ceremony to be attended by foreign journalists.
Journey to North Korea's nuclear heart
A group of Western, Russian and Chinese journalists have been invited by the North to its remote Punggye-ri nuclear test site ahead of its demolition.
They were flown into the North Korean port city of Wonsan but their onward journey was postponed by bad weather, Tom Cheshire from the UK's Sky News tweets.
The site, in the country's mountainous north-east, is thought to be the North's main nuclear facility and the only active nuclear testing site in the world.
Testing has taken place in a system of tunnels dug below nearby Mount Mantap.