Unidentified assailants set ablaze one of the few churches in Yemen's second city Aden on Wednesday, a day after it had been damaged by vandals, witnesses said.

The masked arsonists torched St Joseph, a Roman Catholic church in the central Crater neighbourhood of the port city, which is controlled by loyalists of the exiled government.

A security official said the attackers could be militants of Al-Qaeda.

"The church is in flames," resident Moetaz al-Maysour told AFP, adding that "masked men started the fire."

Yemen's population is 99 percent Muslim.

Of the 22 churches that operated in Aden when the city was a British colony before 1967, only a few remain open, used rarely by foreign workers and African refugees.

Al-Qaeda militants have been accused of several attacks since pro-government forces pushed Iran-backed rebels out of the battle-scarred city in July with support from a Saudi-led coalition.

The jihadist network's Yemen branch, regarded by Washington as its deadliest, has exploited the fighting to boost its presence in swathes of the south and east.