At least 40 people have been killed in three days of fighting between Shi'ite Muslim rebels and Sunni tribesmen, sources on both sides said on Sunday, as sectarian fighting that flared up in October in the north drew closer to the capital Sanaa.

Fighters loyal to the Shi'ite Houthi tribe, who have repeatedly fought government forces since 2004, are trying to tighten their grip on the north as Yemen - home to one of al Qaeda's most active branches - moves towards a federal system that gives more power to regional authorities.

Gulf states and the US are particularly concerned about violence in the country as it shares a long border with top oil exporter Saudi Arabia and its coast runs alongside Red Sea and Gulf of Aden shipping lanes.

Fighting on Friday and Saturday in Al-Jawf province, about 140 km (90 miles) north-east of Sanaa, claimed more than 30 lives before government mediators managed to broker a truce.

And clashes on Sunday in Hamdan, an area some 30 km north-west of Sanaa has killed more than 10, officials on both sides said. Fighting is still going on, they said.

The Houthis - who control much of the northern Saada province bordering Saudi Arabia and next to Al-Jawf - also blew up a three-storey Sunni religious education centre in Hamdan on Sunday, local tribal sources said.

A local official called on government mediators to try to stop the fighting and warned in a statement carried by Yemeni media that failure to do so would result in a "bloodbath".

The Houthi fighters arrived in Hamdan from northern Yemen to safeguard access from their northern stronghold of Saada to Sanaa, where they have large following, tribal sources said.

They said they had no intention of entering the capital.

Fighting in the north erupted last year when the Houthis accused Sunni Salafis at the town of Dammaj of recruiting foreign fighters to prepare an attack. The Salafis said the foreigners were students who had come to study Islam.

The fighting ended with the Salafis agreeing to leave.  - Reuters