British diplomats in North Korea have been warned the government there cannot guarantee their safety after April 10 in the event of conflict, the Foreign Office has said.
The latest move comes amid spiralling tensions in the Korean peninsula.
The Foreign Office says it is "considering next steps" after the North Korean regime asked if Britain is considering evacuating its embassy.
On Thursday, David Cameron said he was "very concerned" about North Korea.
The UK prime minster cited the nuclear threat posed by the regime led by Kim Jong-un as one of the reasons he is committed to maintaining a round-the-clock submarine-based nuclear missile system.
As a result of the latest development, the Foreign Office says it is "considering next steps", including the possibility of amending travel advice.
But it warned North Korea that it had obligations under the international Vienna convention to protect diplomatic missions and claimed the move was an example of the "continuing rhetoric" against the United States.
Anecdotal reports from inside the North Korean capital, Pyongyang, say the mood there is calm, and many believe North Korea is deliberately trying to create a sense of crisis, says the BBC's Lucy Williamson in Seoul.