The United Nations warned Monday of an increased threat of attacks from Somalia's Al-Qaeda-linked Shebab as a major offensive launched against them this month gathers pace.
"Coinciding with the offensive and even ahead of it, Al-Shebab have become more active," UN envoy to Somalia, Nicholas Kay, told AFP.
"They feel threatened and endangered, and so they have carried out significantly more terrorist attacks in Mogadishu in the last couple of months."
UN-mandated African Union troops have been battling Shebab militants in Somalia since 2007, but earlier this month launched a fresh offensive, fighting alongside Somali government forces.
Kay said the operation is pushing the rebels out of key bases, which could prompt them to stage attacks in Mogadishu, as well as other countries in the region such as Uganda and Kenya.
Security sources report some Shebab members are fleeing to mountains in northern Somalia's Puntland region, but some foreign fighters may seek to cross to Yemen, or flee southwards into neighbouring Ethiopia and Kenya.
"They're fleeing into the bigger cities, there are more of them entering Mogadishu," Kay added.
"Some of them are looking to flee perhaps the country and are heading to the remoter corners," he said, speaking after an AU peace and security council meeting in the Ethiopian capital.
- Lacking attack helicopters -
Shebab gunmen have largely fled ahead of the AU advance, only to later stage guerrilla attacks.
But the Islamists have also vowed to retaliate against the troop-contributing nations, with soldiers in the 21,000-strong force coming from Burundi, Djibouti, Ethiopia, Kenya, Sierra Leone and Uganda.
In Kenya, where the Shebab claimed responsibility for the massacre of at least 67 people six months ago in Nairobi's Westgate mall, police last week arrested two men driving a vehicle packed with explosives in the port city of Mombasa.
Gunmen also killed six in an attack on a church near Mombasa on Sunday.
In Uganda, where the Shebab killed at least 76 people in the capital Kampala in 2010, officials warned last week of Shebab plans to use fuel tankers as bombs.
Kay said the size of the mission was sufficient for the time being, but was in dire need of helicopters. The UN has authorised and funded helicopters, but AU member states have failed to provide them.
"What is needed, and has been needed for a long time, are helicopters," Kay said. "It is up to African Union member states to come forward with transport and attack helicopters."