SANAA (AFP) ― At least 60 people were killed in Yemen as clashes raged between Shiite rebels and al-Qaida militants backed by Sunni tribesmen battling for territory in the strife-hit country, sources said Monday.

The rebels, known as Huthis, have been facing fierce resistance from al-Qaida fighters and tribesmen as they seek to expand their areas of control after seizing the capital Sanaa and the Red Sea port city of Hudeida.

A suicide bomber killed 15 people on Monday, including children, when he detonated his explosives-laden car near a rebel checkpoint in the town of Rada, south of Sanaa, witnesses and a tribal source said.

It came after heavy fighting erupted overnight in Rada, a mixed Sunni-Shiite area that has been the scene of frequent clashes.

Twenty rebels were killed in another car bombing that targeted a building where they had gathered and in subsequent clashes, tribal and security sources said, adding that 12 rebels were also captured by al-Qaida militants.

The town was rocked by powerful explosions, with rocket-propelled grenades and artillery used by both sides in several hours of clashes, security officials said.

Ten more rebels were killed during clashes Monday in the Anas district of Dhamar, a Shiite-populated province taken last week by the rebels, said medics and tribal sources.

Meanwhile, 15 fighters from al-Qaida and tribesmen were killed in the Rada clashes, tribal sources said.

Al-Qaida militants also attacked rebel positions northeast of Rada and along a road connecting the town in Baida province to neighboring Dhamar.

Fighters backed by tribesmen also recaptured the town of Udain, in southwestern Ibb province, which they had briefly overran last week in response to the rebels’ advance, a tribal source said.

They then moved towards nearby Ibb city, triggering heavy clashes late Monday with the rebels.

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.

President Abdrabuh Mansur Hadi’s weak Sunni-led central government has failed to stop the rebels, despite a U.N.-brokered peace deal that was supposed to see them withdraw from the capital.

Al-Qaida in the Arabian Peninsula, the extremist network’s powerful Yemeni branch, and Sunni tribesmen have instead fought to halt the rebel advance, leaving dozens dead including 47 Huthi supporters in a suicide bombing in Sanaa this month.

The 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.

Hadi’s government is also a key U.S. ally in the fight against al-Qaida, allowing Washington to conduct a longstanding drone war against the group on Yemeni territory.

The rebels faced no resistance when they took control of Sanaa last month and have refused to leave despite appearing to agree to the naming of a new prime minister under the U.N. deal.

They have since moved south and easily captured Dhamar but have faced heavy fighting in Sunni-majority Ibb province and from al-Qaida in Baida province.

Tribesmen have accused government forces in the area of collaborating with the rebels in their advance.

“Tribesmen are fighting alongside al-Qaida because the army is supporting the Huthis,” a tribal chief said.

On Sunday, negotiations hosted by provincial governor Yehya al-Iryani to convince all fighters to withdraw from Ibb city “failed,” a mediator said.

“The Huthis insisted on deploying their fighters alongside security forces in Ibb ... to fight al-Qaida and prevent it from taking over the province.”

The Shiite rebels have traditionally been concentrated in the northern parts of Yemen, on the border with Sunni-dominated Saudi Arabia.

Yemeni authorities and Saudi Arabia have accused Iran of backing the Huthis in a similar fashion to its support for Lebanon’s powerful Shiite militia Hezbollah.

Gulf Arab states have warned that instability in Yemen is threatening regional security.

Security forces on Monday confiscated scores of motorbikes in Sanaa, enforcing a temporary ban aimed at preventing the use of motorcycles in attacks.