At least 140 fighters have been killed in Yemen in the past week in clashes between Houthis and pro-government forces in the north-central city of Marib, according to military and medical sources.

At least 51 loyalists were killed in the past four days, most of them in clashes in the province of Shabwa and the neighbouring governorate of Marib, multiple military sources told AFP. They also said that at least 93 Iran-backed Houthis died in the fighting and from air strikes by the Saudi-led military coalition backing the government.

The Houthis rarely report casualty numbers, but the figures were confirmed by medical sources.

Last February, the Houthis escalated their efforts to seize Marib, the government's last northern stronghold, and the subsequent fighting has killed hundreds on both sides. Control of the oil-rich region would strengthen the Houthis' bargaining position in peace talks.

According to the military sources, who spoke on condition of anonymity, the Houthis have made advances and seized four districts - one in Marib and three in Shabwa. 

"Three districts in Shabwa have fallen in limited clashes and within hours," one official told AFP.

 Yemen's conflict erupted in 2014 when the Houthis seized the capital, Sanaa, prompting a Saudi-led intervention the following year to prop up the internationally recognised government.

-Agencies