Britons are being warned not to travel to Yemen amid fears that protests against the government could tip the country into chaos.
More than 20 people are said to have died in weeks of unrest over President Ali Abdullah Saleh's 32-year rule.
One of the latest incidents saw state military reportedly fire on a peaceful protest.
The Foreign Office said it was now urging against all travel to Yemen.
"We recommend that all British citizens in the country without a pressing need to remain in Yemen should leave by the commercial flights currently available," a spokesman said.
"Our previous travel advice recommended against all but essential travel to the rest of Yemen, including Sana'a and Aden due to the threat of terrorism, kidnapping and tribal violence. It also advised against all travel to Sa'ada."
President Saleh has made several concessions since the unrest began, including saying he will step down in 2013, but the protesters are demanding his immediate departure.