Human Rights Watch says an unidentified militia fired on a hospital where rebel soldiers held a position in the southern Yemeni province of Lahj, causing damage and endangering medical personnel.

The report released Saturday says Yemeni soldiers aligned with Shiite Houthi rebels deployed snipers last week and later positioned a tank next to the hospital's entrance. It says opposing gunmen started attacking last Monday.

Joe Stork, HRW's deputy Middle East and North Africa director, said both sides "have unlawfully put a hospital in the middle of a battle." Targeting medical facilities is against the laws of war.

Lahj is 35 kilometers (21 miles) north of the port city of Aden. Ground fighting has been fiercest in Aden, where rebels and allied military units are trying to take the city.