About 80 Royal Marines are on standby off the coast of Yemen to assist with the possible evacuation of British civilians. According to Naval sources, the marines are thought to be aboard a naval support ship, RFA Fort Victoria near Yemen. The Ministry of Defence said British military assets were in the region but it did not comment on their exact operational task. Yemen has been affected by weeks of political instability and violence.Yemen President Ali Abdullah Saleh, who has ruled since 1978, has refused to leave office despite protests and a tribal uprising which has brought the country to the brink of civil war and resulted in more than 350 deaths.According to Naval sources, as well as Fort Victoria, another support vessel, RFA Argus, has also been operating in the region near Yemen but is being replaced by the RFA Cardigan Bay, an auxiliary landing ship which is on its way. British Foreign Secretary William Hague said he is worried about the situation in Yemen and urged any remaining Britons in the country who are thought to number a few hundred to leave immediately while commercial flights were still operating.