Saudi-led air strikes targeting Iranian-allied Houthi forces intensified in Yemen on Tuesday, residents said, an escalation of a nine-month-old war that follows a rise in tensions between the kingdom and Tehran.

After weeks of a relative lull, large air strikes targeted military positions linked to Yemen's ascendant Houthis in the capital Sanaa, the port city of Hodaida and the disputed southwestern city of Taiz.

Heavy shelling resumed on battle fronts which had been largely static during a truce which began on December 15 in tandem with UN-backed peace talks.

Houthi fighters launched Katyusha rockets at the city of Marib, residents said, their first attack on the area since Gulf Arab troops and armed loyalists of President Abd-Rabbu Mansour Hadi seized it from the group over the summer.

Houthi forces also advanced against government militiamen in the northwestern province of Hajja and the far southern province of Lahj, reversing recent gains made the coalition.

A military coalition led by Saudi Arabia and its allies has been fighting Yemen's Shia Houthi movement in Yemen to repel what it sees as creeping influence by the group's ally, Iran.

The kingdom on Saturday announced the end of the truce, which had reduced fighting but had been repeatedly violated by both sides.

Earlier the same day, Saudi Arabia executed a dissident Shia cleric convicted of "terrorism". This led to attacks by Iranian protesters on Saudi missions and the severing of ties with Iran by the kingdom in a diplomatic crisis that may deepen sectarian tension in the region

Nearly 6,000 people have been killed since the Saudi coalition entered the conflict in March, almost half of them civilians. The war has exacerbated hunger and disease in Yemen, the Arabian Peninsula's poorest country.