Anti-government protesters shout slogans as they demonstrate to denounce violence in Sanaa, May 25. (Khaled Abdullah/Reuters)

The U.S. State Department Tuesday ordered nonessential diplomats and family members of American government employees to leave and urged private citizens to do so as well, saying “violent clashes...may escalate without notice,” according to Bloomberg.

Fighting had erupted Monday in Sanaa after President Ali Abdullah Saleh refused for the third time to sign a pact mediated by Gulf neighbors that would have him step down, Reuters reported.

Saleh and analysts alike are now warning that the clashes between government forces and opposition tribesmen could drag the country into civil war. The fighting, which has left 40 dead since Monday, has increasingly played out along tribal lines, with the tens of thousands of peaceful protesters largely absent.

For that reason, few videos have been shot by protesters, but here is a video by al-Jazeera on the clashes:

The State Department and Yemeni citizens tweeted about the violence:

#Yemen: We urge U.S. citizens not to travel to Yemen & U.S. citizens currently in Yemen depart while commercial transport is available.less than a minute ago via web Favorite Retweet ReplyTravel - State Dept

Thank God bombing stopped. Yesterday felt like war. God save #Yemenless than a minute ago via Twitter for iPhone Favorite Retweet ReplyTeh Louie

#AliSaleh You cannot simultaneously prevent and prepare for war. #Yemen #Saleh #GCCless than a minute ago via web Favorite Retweet ReplyAbe Alansy