Even if the Kenyan military succeeds in capturing the port, its exit strategy is far from clear. Already, the Kenyan forces, which have never fought a war like this before, appear unexpectedly bogged down.
Kenya is pressing its attack on 10 Somali towns on the approaches to Kismayo. It's made clear that its aim is to seize the city, Somalia's main southern seaport and Shabab's most lucrative possession. The United Nations estimates that port revenues provide Shabab up to $50 million a year, or roughly half of its total funds.
On Monday, the Kenyan and Somali governments issued a joint appeal for international support in blockading Kismayo until Shabab's grip on the city is broken. But the role of other countries in the Kenyan offensive is unclear, though the United States believes Shabab is an al Qaida affiliate and that Somalia is a front line in the war on terror.
Kenya blames Shabab for a string of recent kidnappings targeting Western aid workers and tourists inside Kenyan territory. Shabab has denied responsibility but has threatened revenge attacks in Kenya's capital, Nairobi, East Africa's most important city. Last week, a Kenyan citizen confessed to being a member of Shabab and planning two grenade attacks on Oct. 24 in Nairobi. The youth, a Muslim convert from Kenya's rural western provinces, was promptly sentenced to life imprisonment.
With no roads in much of the Somali countryside, heavy rains have slowed Kenya's tank-equipped infantry to a near halt. That's left most of the offensive to Kenya's air force, the region's strongest, while Kenyan-trained Somali government troops and friendly militias have led the way on the ground.
Reached by phone, residents of Kismayo say that their city has been under steady aerial attack since the Kenyan offensive began Oct. 16. Abdirizak Ahmed, 31, said people are fleeing areas near the port and near Shabab encampments for fear of becoming collateral damage. But the rains have hampered them, too.
"With all this rain we cannot flee out of Kismayo, but we are adapting quickly to the situation by leaving areas close to Shabab," said Ahmed, who lives in the Hangash neighborhood near the Kismayo seaport.
To date, Shabab forces have avoided direct contact with the Kenyan troops, preferring instead to ambush Kenyan supply lines, a likely sign of the guerrilla tactics Kenyan forces would face if their invasion becomes a drawn-out affair.
But that's unlikely to be the case as the first major battle shapes up between the Kenyans and Shabab forces at Afmadow, an important trade hub about 50 miles north of Kismayo that the Kenyan military says it is preparing to capture and Shabab forces are congregating to defend.
Besides Afmadow and Kismayo, the Kenyan military also has targeted Burgavo, a corridor for fishing and charcoal trades, and has overrun Ras Kamboni, a port town near the Kenyan border that's considered a launching pad for the lucrative piracy trade.
According to residents reached by phone, the Shabab have called in hundreds of fighters from other regions of Somalia to counter the assault. Some of the Shabab reinforcements are believed to have been redeployed from Mogadishu, which the rebels largely abandoned in August.
The effects of the military campaign are evident in Kismayo's streets, said Hussein Abdi, 24, who said injured fighters are streaming into the town.
Amal Khalif, a 38-year-old mother of six from Kismayo's Aalenley neighborhood, said the Shabab leadership appears to be making a last-minute attempt to bolster local goodwill, which had suffered from the group's ultraconservative interpretation of Islamic theology that led to bans on a wide range of popular items, from bras to music.
"They are trying to be nice to people now that things have turned worse for them," Khalif said. "I have seen them of late trying to win the trust of the public by treating them kinder and releasing some prisoners, especially youths they have jailed for petty issues like haircut styles and those they accuse of indiscipline towards their men."
But while she hopes to be freed of Shabab rule, she worries about the damage likely to be caused by a prolonged battle for the port's control.
Vanquishing the Shabab in Kismayo is unlikely to lead to stability for the city's residents, many there say. Once in control, Somalia's government will have to contend with the demands of local semi-autonomous administrations and clan warlords also seeking a cut of the revenue pie.
How the government would keep control of the port also is an open question. Kenya and Somalia have called for the expansion of the African Union's peacekeeping force, now numbering 9,000 troops, primarily from Uganda and Burundi, to patrol areas wrested from Shabab control.
But the Somali government is suspicious that Kenya might want to leave troops behind to create a buffer zone against the possibility of a Shabab return. The Somali government fears such a buffer zone would turn into another semi-autonomous region outside its control, similar to Puntland in the country's north, which has operated autonomously for years.
An extended stay by Kenyan troops also could end up promoting a Shabab renaissance, as nationalist forces flock to battle a foreign invader. That's what happened after 2006, when Ethiopia invaded with strong U.S. military backing to take down the Islamic Courts Union, a coalition that had succeeding in taking power in Mogadishu and establishing some semblance of law and order.
Shabab then was a minority extremist wing of the ICU. But it pulled back to the south and launched a heavy insurgency against the Ethiopian occupiers, who later pulled out, unable to quell the rebellion.
Kenya hopes this time will be different, in part because Somalis don't share the same levels of historic antagonism against Kenyans as they do against their archrival Ethiopians, but also because analysts believe that Shabab is weakened. But that doesn't stop some analysts from believing an extended Kenyan presence could become a Shabab rallying cry.
By all assessments, the Kenyan incursion has been bad for aid efforts for the estimated 750,000 people in southern Somalia in danger from starvation because of the area's prolonged drought — the current rains came too late to be of any value to farmers.
Oxfam International, an aid group, has called for diplomatic engagement, saying that "in the past military action in Somalia has had a negative impact on civilians and further reduced access for aid agencies."
The medical relief group Doctors Without Borders said that a Kenyan air assault Sunday on the town of Jilib killed five civilians. Kenya's military says the airstrike was targeting a Shabab camp next to a camp for famine victims. Kenyan Prime Minister Raila Odinga promised to investigate the civilian deaths.
(Boswell and Yusuf are McClatchy special correspondents.)
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