Britain is temporarily withdrawing part of its embassy team from Yemen due to the security situation in the country, the Foreign Office has announced.
Dozens of people are thought to have been killed in weeks of anti-government demonstrations.
The Foreign Office (FCO) said it feared further violent protests on Friday and would therefore leave only a small core staff in place in the capital Sanaa.
The FCO continues to advise against all travel to Yemen.
It is also urging any British nationals currently in the country to leave as soon as possible by commercial means.'Rapid deterioration'
On Friday, doctors in Sanaa told the BBC that unidentified gunmen firing on an anti-government rally had killed at least 45 people and injured 270.
The demonstrators are calling for corruption and unemployment to be tackled and demanding the president step down.
Some 40% of the population live on $2 (£1.20) a day or less in the country, and a third face food shortages.
In a statement on Wednesday night, the FCO said: "In light of the rapid deterioration in the security situation in Yemen and the high risk of increased tension in Sana'a and likely protests on Friday 25 March which might result in violent clashes, part of the British Embassy team in Sanaa is being temporarily withdrawn, leaving a small core staff in place.
"This will take immediate effect."
Yemen is one of a number of countries in the region that have seen unrest since the presidents of Egypt and Tunisia were ousted in popular revolts.
The UK government has urged all parties in Yemen to exercise restraint and to work towards political and economic reform.