At least 15 were killed and 10 others wounded as army troops loyal to the Shiite Houthi group were hit by bombs in Yemen's southern province of Lahj on Monday evening, a government official told Xinhua.

"Suspected al-Qaida terrorists planted explosive device on a bicycle and the device exploded at a military site manned by pro-Houthi forces in Houta city, Lahj's provincial capital, killing 15 soldiers and injuring 10 others including five civilians," the local government official based in Lahj said on condition of anonymity.

A military intelligence source in Lahj confirmed to Xinhua that an improvised explosive device attached to a bicycle exploded at around 8:30 p.m. (1730 GMT) at an army post that joined fighting alongside with with Houthi gunmen in Lahj.

The casualties were shifted to Ibn Khaldoon hospital and some injured were in critical condition, he added.

The Yemen-based al-Qaida in the Arabian Peninsula (AQAP) claimed the bombing attack later in a statement posted on the group's official account on Twitter.

Meanwhile, fierce battles continued on Monday between pro-Houthi forces and tribal militia loyal to Yemen's President Abd-Rabbu Mansour Hadi in the southern port city of Aden and several other provinces, including the oil-rich southeastern Shabwa province amid intensified airstrikes by the Saudi-led coalition forces.

The pro-Hadi tribal militia took over control of two army brigades that were guarding oil facilities in Belhaf area of Shabwa after fierce fighting with Houthis, local security sources said.

The security sources said that dozens of people were either killed or injured from both sides as the fighting continues in Shabwa on Monday night while Saudi-led air raids bombed a number of Houthi-controlled positions there.

Spokesman of the Yemeni government Rajeh Badi said that the former prime minister Khaled Bahah was sworn in as vice president on Monday at the Yemeni embassy in Riyadh, one day after he received appointment of Hadi.

The security situation in Yemen has sharply deteriorated since early March when conflicts erupted in several provinces in the country's southern regions.

A coalition led by Saudi Arabia started late last month air strikes on Houthi targets in the Yemeni capital of Sanaa and other cities, saying the multinational action is to protect President Abd-Rabbu Mansour Hadi's legitimacy and force the Houthis to retreat from cities they have seized since September 2014.

The fighting across the country and three-week airstrikes have left more than 500 people killed, 2,000 wounded and forced hundreds of thousands of families to flee their homes