SANAA (Reuters) - Suspected Islamist militants blew up a gas pipeline in eastern Yemen on Monday for the third time in recent months as the government ratcheted up its campaign against al Qaeda linked insurgents in the south.

The latest attack will likely delay plans to resume LNG output which had been halted by another attack in April claimed by Islamist militants.

The $4.5 billion Yemen LNG project has two production trains with a combined capacity of 6.7 million metric tonnes (7.3 million tons) per year, supplying mainly to Asia, and then to Europe and Americas.

"The explosion took place at three a.m. this morning in a desert area in Shabwa governorate," said a Yemen LNG employee, adding it would now take weeks for output to be restarted.

"We immediately suspect al Qaeda as they claimed responsibility for the last two attacks on the pipeline," he said, speaking on condition of anonymity.

On March 30, the same gas pipeline was blown up in retaliation for the killing of five Islamist militants in a U.S. drone strike.

Residents said flames could be seen from several kilometers away. The militants exchanged gunfire with an army brigade charged with guarding the pipeline following the blast, a local security official in Shabwa said.

Yemen's oil and gas pipelines have been repeatedly sabotaged since anti-government protests broke out in January 2011. Since then, militants have exploited weak central government control to seize swathes of territory and several towns.

President Barack Obama's counter-terrorism adviser flew to Yemen on Sunday, coinciding with a fresh offensive against militants in the south after Washington said it had foiled a plot by al Qaeda's Yemen-based affiliate to blow up an airliner.

The pipeline transports LNG from Maarib to an export facility at Balhaf. The export terminal opened in 2009 and is led by French oil major Total with three South Korea companies holding stakes.

(Reporting by Tom Finn; Writing by Isabel Coles)