The Yemeni army is gearing up for a push to try to take a southern coastal town from al-Qaeda-linked fighters, local residents say.
Hundreds of troops backed by tanks were closing in on the al-Qaeda Arabian Peninsula (AQAP)-held town of Shaqra, about 50km along the coast east of Zinjibar, residents there said.
Via text message, the head of the southern military zone asked people living in the area not to use the roads around Shaqra and two other towns controlled by the fighters.
Shaqra lies along a major shipping route that is also the gateway for Somali fighters entering the country.
Yemen's defence ministry said fierce clashes had killed at least 23 al-Qaeda fighters, the Associated Press reported.
A statement from the ministry on Tuesday said fighting between government troops, backed by heavy artillery, and the fighters intensified overnight in the northern part of Zinjibar, which is the capital of Abyan province.
The ministry said Pakistani and Somali nationals were among the slain fighters.
Peter Neumann, professor at King's College in London, told Al Jazeera: "All these people, whilst being al-Qaeda, are also anti-government, and it is often not so easy to distinguish between the two because al-Qaeda is so immersed in tribal structures in the South of Yemen."
"It has become virtually indistinguishable from a normal insurgent force," he said.
Neumann said that made it complicated for the US and Yemeni governments to dislodge them from their strongholds.
Al Jazeera’s Hashem Ahelbarra, reporting from the frontline in the southern town of Zinjibar, the capital of Abyan province, said on Monday: “The army has taken up positions here. They are backed by thousands of tribal fighters, air force and drone attacks.
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“The problem they say [they face] is al-Qaeda using guerilla warfare tactics making it extremely difficult for the Yemeni army to put an end to the presence of al-Qaeda, which has gained more territory in the southern part of Yemen.”
The US is backing the offensive in the south and has stepped up its campaign of drone strikes on alleged al-Qaeda members.
It has also sent dozens of military trainers and stepped up aid to Yemen where it wants President Abd-Rabbu Mansour Hadi to reunify the military and fight AQAP.
Speaking to Al Jazeera near the frontline, Colonel Ali Radman Qahtan of the Yemeni army said: “The biggest challenge we face is that al-Qaeda fighters are constantly on the move in small numbers, they never hold out in one place.
“It’s an army fighting militias, they know the area very well ... and take advantage of the dense trees to move surreptitiously."
The army also clashed with AQAP in the town of Jaar, about 30km to the north.