Yemeni troops have clashed with al-Qaeda fighters in an effort to dislodge them from the southern town of Zinjibar.
At least six fighters were killed in the clashes on the eastern edge of the town in the province of Abyan, the defence ministry said on Monday.
Several al-Qaeda fighters were also killed on Monday in air strikes in other areas of southern Yemen. Local officials and fighters said one of the attacks was carried out by a US drone.
Fighters overran Zinjibar one year ago, while former president Ali Abdullah Saleh grappled with protests that weakened central government control over Yemen and eventually toppled him.
The town has been contested ever since and previous efforts to retake Zinjibar have met with fierce resistance from the fighters.
The US and its Gulf Arab allies have watched with mounting alarm as security deteriorates in Yemen, home to al-Qaeda's Arabian Peninsula wing (AQAP), which is viewed by Washington as a serious threat.
An al-Qaeda bombing attack on May 21 killed over 100 people in the capitol of Sanaa.
The Yemeni army has recently regained some initiative in the south, pushing into the centre of Zinjibar, but the fighters
still hold a considerable chunk of the town and have planted mines to cover their retreat, officials said.
Jaar, another stronghold for fighters in Abyan, is being surrounded from all sides by the army.
US intelligence and counter-terrorism officials say their ability to conduct operations inside Yemen has improved significantly since PresidentAbd-Rabbu Mansour Hadi replaced Saleh earlier this year.
A local official said seven al-Qaeda operatives had been killed in an air strike targeting a vehicle on the road between
the town of Azzan and Mukalla, the capital of Hadramout province in the east.
Earlier, several fighters were killed in an air strike in al-Baydah province, north of Abyan, the defence ministry said.
Local sources described the attack as a US drone strike.
A local official said the target of the strike was a provincial militant commander and his brother, both of whom survived.
US drones have frequently killed civilians and are deeply resented by Yemenis.
US Defence Secretary Leon Panetta on Sunday defended the use of drones in an interview with a US news show, saying that they were "the most precise weapons" the US had.
His comments marked the first time the US had formally acknowledged the use of unmanned drones against al-Qaeda suspects in Yemen.