Fighting between separatists and government forces in southern Yemen has killed at least 36 people, the Red Cross says, while the president accuses the fighters of a coup.
About 185 people have been wounded.
President Abd Rabbu Mansour Hadi is calling for a cease-fire, saying "rebellion and weapons won't achieve peace or build a state."
He said the real enemy is the Iranian-backed Houthi rebels, and anything else distracts from that fight.
Fighting broke out when Hadi ignored separatists' demands to fire Prime Minister Ahmed Obaid bin Dagher, accusing him of corruption.
A spokesman for the Saudi-led coalition that backs Hadi is calling for restraint by the separatists and for the government to listen to their "political and social" demands.
The separatists are backed by the United Arab Emirates. They want to bring back the independent country of South Yemen. The fighters have seized several government buildings in the port city of Aden, which is serving as the capital of Hadi's internationally-recognized Yemeni government.
South Yemen was an independent state before its unification with North Yemen in 1990.
All of Yemen has been in turmoil since Houthi rebels seized the capital of Sana'a in 2014, forcing Hadi to flee to exile in Saudi Arabia. Hadi has remained there while his government operates out of Aden.
Saudi-led coalition airstrikes looking to oust the Houthis have obliterated entire civilian neighborhoods, including schools and hospitals. Yemen is also battling a deadly cholera outbreak and a possible famine. The U.N. estimates about 80 percent of Yemenis are in desperate need of food, medicine and clean water.