Yemeni medical officials and residents say that shelling killed 20 civilians at a busy market in a rebel-controlled western city the previous day.

The officials said on Friday that the deaths took place in Taiz, one of the worst-hit cities in Yemen's conflict where fighting between Shiite rebels known as Houthis and forces loyal to the internationally recognized government escalated this week.

The government forces have pushed the Houthis out of several districts of the city, known for its cultural heritage.

Doctors Without Borders said on its official Twitter account that one of the victims of Thursday's shelling worked for the aid group.

The officials and the residents spoke on condition of anonymity because they weren't authorized to speak to reporters.