The United States has ordered all non-essential diplomats and embassy family members to leave Yemen amid mounting violence between loyalists and opponents of President Ali Abdullah Saleh.
The State Department said on Wednesday the security threat level is extremely high due to terrorist activities and civil unrest throughout the Middle East country, with large-scale protests in major cities.
Clashes between Yemeni loyalist forces and protesters demanding an end to Ali Abdullah Saleh's 33-year rule have flared after the collapse of a transition deal, Reuters reports.
The deal mediated by Gulf neighbours would have given Mr Saleh immunity from prosecution, but on Monday he refused to sign it.
In March, the US told its citizens to avoid travelling to Yemen and said those already there should consider leaving due to deteriorating security.
Fresh clashes in capital
At least 20 people have been killed in fresh clashes in the capital Sana'a overnight on Wednesday as fighting intensifies between government forces and the country's most powerful tribal group.
It is estimated that 80 people have been killed since the violence erupted three days ago.
The BBC reports the fighting appears to have spread in the district where the tribal leader Sheikh Sadiq al-Ahmar has his compound to other areas in the north of the city.
Government forces have shelled and put out of action a key opposition television station. The tribal fighters still appear to have control of several ministries.
President Saleh has ordered the arrest of Sheikh Sadiq al-Ahmar.