ADEN, Yemen - A group of gunmen attacked Tuesday two military checkpoints in southern Yemen, triggering a fierce firefight with army forces that lasted several hours in the province of Lahj, a local security official said.

Several gunmen launched an armed attack with assault rifles and home-made grenades on two key military checkpoints in Lahj's suburbs, the official told Xinhua on condition of anonymity, adding that there were no immediate reports of casualties among the soldiers.

"The attacks have been repelled. All armored army brigades stationed around and in Lahj province are on high alert," the official said.

The assailants are believed to belong to the Yemen-based al-Qaida offshoot.

Besides Lahj, Yemeni authorities are also searching for them in the neighboring province of Abyan, which used to be the terror group's stronghold in the country, according to the official.

Witnesses told Xinhua anonymously that there were sounds of heavy gunfire and explosions at the scene of the attacks.

Meanwhile, militants of the al-Qaida terrorist group bombed early on Tuesday a gas pipeline feeding the country's only liquefied natural gas (LNG) export terminal, Yemeni officials and oil engineers told Xinhua.

Tuesday's attacks occurred despite the Yemeni army's claim that it has won its fight against the al-Qaida militants, who were responsible for numerous acts of violence in the Arab country during the past two years.

A string of high-level assassinations struck Yemen's southern regions over the past few months, targeting intelligence and security figures who hunt al-Qaida militants, after government troops drove dozens of terrorists from their main strongholds in Abyan province.