A US air strike killed at least eight policeman in Afghanistan's Helmand province, a government official said on Friday, the latest casualties from a rise in air and ground operations against the Afghan Taliban.

A air strike by the Saudi-led coalition against a radio station in Yemen's Houthi-held port city of Hodeidah killed four people on Sunday, residents and medical sources said.

The bombing on a crowded market in rebel-held northern Yemen killed a total of 51 people, according to the Red Cross.

Fifty-six children were also among the 79 people wounded in the Thursday strike on Saada province, a rebel stronghold that borders Saudi Arabia.

At least 29 children were among those killed in the air raid on Thursday on a bus in a crowded market in Dahyan, Saada province, according to the International Committee of the Red Cross.

The coalition said it had carried out what it called "legitimate military action" in the area targeting Houthi rebels.

Yemeni government forces backed by a Saudi-led coalition have been conducting an offensive to capture Hodeida from Iran-backed Houthi rebels.

Hamas sources said the casualties were security men working at an observation post near Rafah, in the southern Gaza Strip.

An air strike on one of the last holdouts of the Islamic State group in Syria has killed 54 people, more than half of them civilians, a war monitor said on Friday.

The US military said in Washington it had carried out a strike aimed at a senior militant figure in the eastern Afghan province of Kunar.

Doctors Without Borders said Monday it had "temporarily frozen" operations in a rebel-held area of northwestern Yemen following an air raid on a cholera treatment centre it supports.

A woman was among four people killed in an air strike that hit a petrol station in Yemen's rebel-held capital late Saturday, medical sources said.