Yemeni government forces clashed with separatists in the southern port city of Aden on Sunday.
An Associated Press journalist heard heavy gunfire in the Khor Maksar district, while thick black smoke rose in the sky after an airstrike.
Witnesses, speaking on condition of anonymity because they feared reprisal, said residents were fleeing the area. Schools and universities were shut down and students were told to stay home.
President Abed Rabbo Mansour Hadi’s forces, which have been at war with Shiite rebels known as Houthis since March 2015, deployed across the city to prevent protests by southerners who want to bring down his government and separate from the Houthi-dominated north.
The protests are being led by Aidarous al-Zubaidi, a former Aden governor backed by the United Arab Emirates. The UAE is a key member of the Saudi-led coalition allied with Hadi’s government, but has had tense relations with the president.
The UAE has trained and armed forces, known as the Security Belt, who do not answer to Hadi’s government.