Yemeni rebels say they are to withdraw from a key city they seized in an advance towards Yemen's capital and an army unit will now move into Amran.

Amran has seen fierce fighting since February as the Shia Houthi rebels, known as Ansarullah, advanced from their mountain strongholds towards the capital Sanaa.

"Our men will withdraw from Amran as soon as an army unit moves in," Mohammed Abdessalam, rebel spokesman, said on Saturday.

He said the decision to pull back from Amran, 50km north of Sanaa, came in a deal struck with the Defence Ministry.

"Other military units that are under the authority of the Defence Ministry will follow suit."

On Friday, the 15-member UN Security Council unanimously called on the Shia rebels to leave Amran.

A statement by council members said the fighting impeded a political transition in Yemen, threatened to impose sanctions on those impeding it and called on all fighters to disarm.

Three-day battle

Amran, home to an estimated 120,000 people, fell to the rebels on Tuesday after a three-day battle that the Red Crescent says uprooted some 10,000 families.

By seizing Amran, the rebels had made a major advance towards Sanaa, posing a threat to President Abd-Rabbu Mansour Hadi's government.

The rebels say a federalisation plan, approved in February after national talks as part of a political transition, would divide Yemen into rich and poor regions.

Yemen is struggling with violence and lawlessness after Ali Abdullah Saleh was forced to step down from the presidency in 2011.

In the country's west, tribesmen on Saturday bombed the country's main oil export pipeline, halting crude flows, according to local officials.

The attack hit the pipeline which carries crude from the Safer oilfields, in the al-Habab area of Maarib province, to Ras Isa oil terminal on the Red Sea, the officials said.

The pipeline carries about 70,000-110,000 barrels per day of Marib light crude.

It was repaired in late May after a previous attack by tribesmen.

Yemen's oil and gas pipelines have repeatedly been sabotaged by rebels or tribesmen since 2011, causing fuel shortages and cutting export earnings for the country.

Tribesmen carry out such assaults to press the government to provide jobs, settle land disputes, or free relatives from prison.