By Abdi Sheikh
MOGADISHU (Reuters) - Hundreds of Somali al Shabaab militants poured into the southern port city of Kismayu on Wednesday raising fears of a bloody showdown with African Union soldiers for control of the rebels' last bastion, residents said.
The al Qaeda-linked insurgents drove convoys of machinegun-mounted pickup trucks into the city and set about building defenses, witnesses said.
Somalia is a hotspot in the U.S.-led war on militant Islam and al Shabaab is the most powerful of an array of militias spawned by two decades of conflict - threatening regional stability.
The reinforcements came a day after locals said al Shabaab commanders had pulled out of the city leaving a small number of soldiers to defend the stronghold.
Rumors swirled though Kismayu's winding alleyways that one of the militants' top three commanders was now in the city.
"Al Shabaab fighters have filled the bases and camps they abandoned in the past few days," said butcher Farah Roble.
"We're terrified. Al Shabaab looks determined to fight for Kismayu," he said.
Earlier this week, Kenyan forces overran several militant outposts to the north and southwest of Kismayu, pushing to within 50 km (30 miles) of Somalia's second biggest city.
Kenyan military spokesman Colonel Cyrus Oguna said the final assault on Kismayu was inevitable.
"We are very, very near Kismayu. It is not a tarmac road that we are walking on. We have to be cautious, the way is littered with explosives. Nevertheless, it will happen. Kismayu will fall," he told Reuters by phone.
Defeat in Kismayu, a hub of al Shabaab operations throughout the group's five-year insurgency, would badly hurt the rebels' morale and weaken their capacity as a fighting force.
However, it might not deliver the knockout blow hoped for by Mogadishu and its regional allies. Western diplomats expect the insurgents to turn increasingly to guerrilla-style hit-and-run raids and urban bombings.
"DUTY TO FIGHT"
Al Shabaab said Kismayu, about 500 km (311 miles) south of the capital Mogadishu, was calm. Its radio station, Radio Andalus, was back on air after broadcasts stopped on Tuesday.
"All offices and businesses are open. We do not fear our enemies. They cannot just dash into Kismayu because we have strong defenses," Sheikh Abdiasis Abu Musab, spokesman for al Shabaab's military operations, told Reuters.
The U.N. refugee agency said about 4,000 civilians had fled Kismayu since Monday. Residents reported on Wednesday that al Shabaab were trying to stop locals fleeing.
"Al Shabaab is taking to the mosques and ordering people to fight. They said Muslims have a duty to fight the African Union forces inside and outside the city," said resident Ismail Sugow.
Sugow said he could hear al Shabaab test-firing their artillery on the city's outskirts.
He said Shabaab had drafted in fighters from nearby Bay, Bakool and Lower Shabelle regions. A second resident said the reinforcements came from "other parts of the country".
Another resident, Hussein Nur, said the militants, who accuse the government of serving only Western interests and want to install a strict interpretation of sharia, Islamic law, were whipping up fear among the local population.
"Al Shabaab said in the mosques 'all Muslims should join the jihad as Kenyan troops will rape your wives and sisters and loot your property'," Nur said.
Kenya sent troops into Somalia, on its eastern border, in October to help crush the militants, and Kenyans are expected to lead AMISOM forces in an eventual assault on the port city.
Al Shabaab has lost strongholds across southern and central Somalia in the past year as AMISOM troops - including Ugandans, Burundians and Djiboutians - advance.
(Additional reporting by Feisal Omar in Mogadishu and Richard Lough in Nairobi; Writing by Richard Lough; Editing by Louise Ireland)