Yemen's army and air force supported by local militiamen and with US backing stepped up an offensive to expel Al-Qaeda from their southern bastions, with fighting concentrated around the town of Jaar on Sunday.
"Violent clashes on Jaar's western outskirts between the army and Al-Qaeda are continuing," a military official said.
Residents said the Yemeni air force launched four strikes on Al-Rabwa, at Jaar's western entrance, and that they saw militants using vehicles to take away the bodies of several militants killed.
Thirteen jihadists were killed overnight, according to tribal sources, while witnesses said 18 vehicles loaded with Al-Qaeda militants were brought in from Azzan in the eastern Shabwa province to reinforce their comrades in Jaar.
Five militiamen fighting alongside the army were also killed and four wounded, the military official said, without giving army casualties.
Residents and tribes in the area surrounding Jaar have formed armed militias, Popular Resistance Committees, to back the army, similar to those formed in other Abyan towns -- Loder and Mudia.
Troops on Thursday took full control of Loder, which militants have been trying to seize for several months.
"The army will also take control of Jaar in the coming days," another military official said. "We want to control Jaar, a major Al-Qaeda stronghold, before Zinjibar," capital of Abyan province and which militants overran last year.
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Yemeni forces launched an offensive on May 12 to capture Al-Qaeda controlled areas in Abyan, where most towns have been under the jihadists' control apart from Loder and Mudia.
Since the offensive began, 213 people have been killed, according to a tally compiled by AFP, including 147 Al-Qaeda fighters, 31 military personnel, 18 local militiamen and 17 civilians.
According to Western diplomats in Sanaa, US experts have been advising the Yemeni army in combat.
John Brennan, US President Barack Obama's top counter-terrorism aide held talks in Sanaa last week with President Abdrabuh Mansur Hadi on "combatting terrorism" and attempts by Yemen's army to crush the local branch of Al-Qaeda.
The offensive was launched after newly-elected Hadi vowed to fight the network and followed days after the White House announced that a plot by Al-Qaeda in the Arabian Peninsula (AQAP) to blow up a US airliner had been foiled.
A senior US official told the New York Times that a bomb for the would-be attack was sewn into "custom fit" underwear that would have been difficult to detect even in a careful pat-down at an airport.
It said a double agent spent weeks with AQAP before handing over information allowing the United States to launch a drone strike on May 6 that killed Fahd al-Quso, a senior figure wanted for the 2000 bombing of the USS Cole in Yemen.
Quso's name figured on an FBI list of most wanted terrorists, along with a reward of up to $5 million for information leading to his arrest.