Yemen has become a stronghold for al-Qaida and other terrorist groups. Reuters

Yemeni soldiers have killed at least 16 al-Qaeda fighters in the troubled southern region of the country, military officials said Monday.

The attacks, which saw Yemeni warplanes bombard a militant hideout 40 miles from the city of Zinjibar, Abyan province, came as six government troops died battling militants in the city itself.

Also on Monday, suspected insurgents blew up a gas pipeline in the east of the country for the third time in recent months, further delaying plans to resume liquefied natural gas (LNG) output at the country's two facilities in Balhaf.

The military has been hard pressed in the restive southern region since Islamic militants overran the provincial capital last year.

Backed by heavy artillery, the military managed to wrest control over some parts of the area from militants during Monday's fighting.

Yemen has become a hotbed for al-Qaeda in the Arabian Peninsula (AQAP) for several years now, with the government suffering a series of humiliating defeats and losing vast areas of the country to the insurgents.

Monday's fighting came after U.S. authorities foiled another plot by al Qaeda to take down a U.S.-bound airliner with an underwear bomb last Wednesday.

The would-be bomber, based in Yemen, had not yet picked a target or bought his plane tickets when the CIA stepped in and seized the device.

The agency received intelligence about the plot in April, adding that the plan was to use an upgraded version of the underwear bomb that failed to detonate aboard a jetliner over Detroit during Christmas 2009.

In the past two weeks, U.S. drone strikes have killed at least three senior al-Qaeda leaders in southern Yemen.

The attacks took place in Marib and Shabwa provinces in the southeast.

The first attack killed seven suspected militants who were travelling in a vehicle which immediately attracted the attention of the government. Residents witnessed thick black smoke, reported CNN.

The second strike was in the oil region of Marib which claimed the lives of four insurgents.