Government troops regained control of a key Al Qaeda stronghold in Yemen's south in a surprise dawn attack on Tuesday, recording their first major triumph over the militant group in more than a year, witnesses and the military said.

Military officials said the attack on Jaar followed hours of heavy shelling of the town by artillery and rockets from hilltop positions. At dawn, troops and allied tribesmen entered the town from three different fronts in trucks, while dozens of tanks were used to block the town's entry and exit points, they said.

Spokesman of the Ministry of Defense Gen. Mohammed al-Quton was quoted by the Yemeni state-news agency SABA as saying that 20 "terrorists" were killed while four of the troops were "martyred." He also said troops also regained control over a vital highway that links Jaar with the port city of Aden after it was blocked for more than a year.

The officials and witnesses said that some 500 Al Qaeda militants fled the town after spraying the town's walls and store shutters with graffiti saying, "Al Qaeda has withdrawn.