Kenyan troops reinforced positions in southern Somalia in preparation for fresh assaults against the Al-Qaeda linked Islamist Shebab militia, army officials said Wednesday.

"Our forces are in good shape to fight this battle to the end," said army spokesman Major Emmanuel Chirchir, on the fourth day since Kenya declared war on the Shebab militia and confirmed it had sent its army across the border.

The main forward base of Kenyan operations is at Qoqani, some 100 kilometres (60 miles) as they prepare to push forward to seize Afmadow, which Somali government forces are fighting to secure.

"Elements of them (Somali government forces) are in Afmadow, and we are working hand-in-hand with them, gathering information and intelligence," Chirchir added.

Heavy air strikes are reported to have been hitting Shebab positions in efforts to dislodge the militants, before Kenyan-backed Somali government ground troops move in to drive out rebels, according to witnesses.

"Our aircraft are involved in the operations," Chirchir said, adding that Kenya was "cooperating" with Somali government forces and aligned militia forces.

Pro-government gunmen from the Ras Kamboni militia group have also been fighting against Shebab insurgents.

Officials said the only Kenyan casualties had been the crash of a military helicopter inside Kenya, reportedly due to mechanical failure.

"In terms of injuries, the first attack saw the death of 73 Shebab, while on our own side the only casualties so far was the coming down of the helicopter, with the death of five Kenyan soldiers," Chirchir said.

However, a police source in the Kenyan border town of Garissa told AFP that there were Kenyan casualties, including both dead and wounded soldiers.

The source did not provide further details and AFP could not independently verify the reports.