* Several others in serious condition
* No one claims responsibility for attack
* Yemen is grappling with multiple challenges (Adds details, background)
ADEN, March 4 (Reuters) - A suicide bomber killed at least 10 members of a pro-government militia that helped the Yemeni army to drive al Qaeda-linked Islamist militants out of southern strongholds in a U.S.-backed campaign last year, a commander said on Monday.
Nizar Jaafar said at least 15 other people had been wounded in the attack on an office of the Popular Committees in the town of Lawdar in the southern province of Abyan. Doctors said they expected the number of fatalities to rise as some of the wounded were in serious condition.
No one claimed responsibility for the attack, but Islamist group Ansar al-Sharia has previously said it carried out similar bombings, often in reprisal for the tribal fighters' role in driving the militants out of their strongholds.
Yemen has been grappling with multiple challenges since a popular uprising forced President Ali Abdullah Saleh out of office in 2011 and brought Abd-Rabbu Mansour Hadi in his place.
Apart from the Islamist militant insurgency, the U.S.-allied country which is next door to the world's top oil exporter, Saudi Arabia, is fighting a separatist movement seeking to revive the Socialist state that merged with North Yemen in 1990, as well as a potential challenge from Shi'ite Muslim rebels known as Houthis in the north.
Ansar al-Sharia has carried out a campaign of suicide attacks against the Yemeni army and its militia allies after they were forced to quit cities they captured in 2011, during the turmoil that accompanied the popular protests against Saleh.
In a separate incident, a local official said that four suspected militants have escaped from a prison in Lawdar on Monday. The official gave no further details.
The United States has used unmanned drones to target the al Qaeda group in Yemen, which has planned attacks on international targets including airliners and is described by Washington as the movement's most dangerous wing. (Reporting by Mohammed Mukhashaf; Writing by Sami Aboudi; Editing by Stephen Powell)