By Mohammad Mukhashaf, Feb. 12, 2015, Reuters.com

(Reuters) - Al Qaeda-linked fighters seized a large army base in a dawn attack in southern Yemen on Thursday, militants and residents said, hours after the United Nations warned that the country was on the brink of civil war.

The base in the southern province of Shabwa, housing a brigade of up to 2,000 government soldiers, fell after several hours of heavy clashes, residents and local news sites said.

The al Qaeda-affiliated Ansar al-Sharia said on Twitter it had set off a suicide bomb at the gate and imprisoned some of the troops.

Al Qaeda and other Sunni Muslim militants have stepped up attacks since rival Iranian-backed Shi'ite Muslim fighters from the north seized the capital in September and started expanding across the country.

The Houthis have sidelined the central government and have clashed with Sunni tribesmen in Yemen, which borders oil giant Saudi Arabia.