North Korea has moved three American prisoners from a labour camp to a hotel ahead of the planned summit with the US, a South Korean activist said.
Academics Kim Hak Song and Tony Kim, and businessman Kim Dong Chul were moved this week to a hotel on the outskirts of Pyongyang following instructions from "superior authorities", campaigner Choi Sung Yong is reported to have said.
They are getting "health treatment" and "ideological education", he added.
A South Korean official is reported to have said their release has been negotiated over the past two months and is "imminent".
The trio, who are not related, were imprisoned in 2016 and 2017 after being accused of espionage or "hostile acts".
Donald Trump gave credence to the claim after he posted a cryptic Tweet on Wednesday night, which said: "As everybody is aware, the past Administration has long been asking for three hostages to be released from a North Korean Labor camp, but to no avail.
Just days before, Mr Trump's new national security adviser John Bolton, told Fox News on Sunday: "If North Korea releases the detained Americans before the North-US summit, it will be an opportunity to demonstrate their authenticity."
US Secretary of State Mike Pompeo is believed to have discussed the prisoners' release during a secret meeting with North Korean dictator Kim Jong Un over the Easter weekend in Pyongyang.
Mr Trump also confirmed last week the US had been negotiating their release.
North Korea experts said Pyongyang was paying close attention to the three prisoners' health to make sure there is no repeat of Otto Warmbier's case.
The American student was imprisoned in North Korea for allegedly stealing a propaganda poster from his hotel room in 2016.
He died six days after being released and sent back to the US in a coma last June.
Last week marked the first time since the Korean War that a North Korean president had stepped foot in South Korea, as Mr Kim met his South Korean counterpart Moon Jae In for the inter-Korean summit.
The two Koreas agreed to work towards denuclearisation, sign a peace treaty to end the Korean War after 65 years, end "hostile activities and resume family reunions.
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At the beginning of March the White House confirmed that President Trump would meet Chairman Kim in late May or early June.
It will be the first time a sitting US President will have met a North Korean leader since the Korean War.