Yemeni troops and a US drone struck positions held by Al-Qaeda suspects and Sunni tribes on Sunday killing over a dozen insurgents who have been battling Shiite rebels, tribal sources said.
President Abdrabuh Mansur Hadi meanwhile urged the rebels to "immediately" withdraw from the cities they have captured, including the capital Sanaa, and criticised the security forces.
The rebels, known as Huthis, captured Sanaa on September 21 with almost no resistance from the security forces.
They have instead been facing fierce resistance from Al-Qaeda fighters and mainly-Sunni tribesmen as they attempted to expand their areas of control beyond Sanaa and the Red Sea port city of Hudeida.
Clashes broke out on Friday evening when Huthi fighters trying to wrest control of the mountains around the central town of Rada, in Baida province, met resistance from Sunni militias, tribal sources said.
On Sunday, the rebels took over several of these areas after a suspected US drone and army jets raided the positions held by Al-Qaeda and the Sunni tribesmen.
One source said "20 Al-Qaeda militants" were killed in the strikes, although the toll could not be independently confirmed.
Violence meanwhile raged in the Rada region of Manaseh, an Al-Qaeda stronghold which was stormed by Huthis on Sunday, tribal sources said.
In a speech aired Sunday on state television, Hadi urged the Huthis to "immediately pull out their armed men from all the cities and provinces (they seized) including Sanaa".
- President slams rebels -
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The Yemeni president slammed the rebels for "trying to take over the role of the state under the excuse of fighting Al-Qaeda in a bid to conquer more provinces," describing their acts as "unacceptable".
Addressing the army, he said: "What has happened during the past month and is taking place today is unworthy of a deep-rooted institution for which the Yemeni people have struggled to be strong... and biased only towards the nation under all circumstances."
He urged troops not to "run away from the national and moral responsibility" facing them and "not be lured," without elaborating.
Hadi is the supreme commander of the armed forces in Yemen.
The rebels took control of Sanaa after orchestrating weeks of protests that paralysed the government.
They then pushed south this month as tribal sources said the Huthi fighters were even assisted by artillery units from the army and air force.
Their advance has taken them out of the mainly Shiite northern highlands into predominantly Sunni areas.
Tribal sources said Saturday that two vehicles carrying suspected Al-Qaeda militants near Rada were struck by a missile fired from an unmanned drone, leaving 10 dead.
Fighting between Shiite rebels and Sunni tribesmen allied to Al-Qaeda has already left dozens dead in central Yemen.
Yemen is a key US ally in the fight against Al-Qaeda, allowing Washington to conduct a longstanding drone war against the group on its territory.
The Huthis have seized on chronic instability in Yemen since the 2012 ouster of long-serving autocratic president Ali Abdullah Saleh to take control of large parts of the country.
The latest fighting has raised fears of Yemen -- located next to oil kingpin Saudi Arabia and important shipping routes in the Gulf of Aden -- collapsing into a failed state.