Kenyan jets struck in Somalia Wednesday in a bid to rid the border area of rebels blamed for a spate of abductions.

Kenyan jets struck in Somalia Wednesday in a bid to rid the border area of rebels blamed for a spate of abductions, including that of a French woman who died in captivity, officials in Kenya said.

Kenyan ground troops guided by pro-government Somali forces prepared for a fresh assault against the Shebab insurgents with the blessing of the Western-backed government in Mogadishu and its Ugandan protectors.

Nairobi's unprecedented military incursion into Somalia, which it said had already killed dozens of Shebab fighters, triggered dire warnings by a top Shebab leader of bloody retaliation.

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.

Analysts say Kenya wants to carve out a buffer zone along the border, but Shebab forces said Wednesday they were preparing a counter-attack.

"We have been gathering information on the Kenyan army's strength, in terms of weapons and manpower," Sheikh Abdulaziz Abu Musab, a Shebab spokesman, said on the group's radio Al-Andalus.

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

"In terms of injuries, the first attack saw the death of 73 Shebab," army spokesman Major Emmanuel Chirchir said, adding that the only Kenyan deaths were five killed in a helicopter crash.

However, a police source in Garissa, on the Kenyan side of the border, stated that there were Kenyan casualties.

Kenya's shock assault against the hardline Shebab has sparked a fierce reaction with the militants warning of reprisals on "all fronts."

Security forces are planning a "major operation in Nairobi to get rid of Al-Shebab," Assistant Security Minister Orwa Ojode said Wednesday, a rare admission from the government the Shebab threat exists even in the capital.

The Shebab deny any involvement in the recent kidnapping of foreigners, which have raised questions about Kenya's ability to host the million tourists who visit each year and one of the world's largest aid communities.

On Tuesday, a car bomb exploded near the foreign ministry in Mogadishu killing at least five civilians, even as two top Kenyan ministers were holding talks nearby to coordinate the ongoing military operation.

On Wednesday, a roadside bomb went off in Mogadishu, injuring two.

Kenya's decision to invade came after a British tourist was snatched from a Kenyan resort last month, the French woman from her beachfront home in Lamu and two Spanish aid workers from Dadaab refugee camp last week.

A French government statement said "the conditions of her detention and the fact that the kidnappers probably refused to give her the medication that we sent her" likely led to her death.

Kenya's assault -- dubbed Linda Nchi ("Defend our Country" in Swahili) -- began without a mandate but Somalia's government and Kenya signed a deal Tuesday to "cooperate in undertaking security and military operations," limiting Kenyan operations to the Lower Juba region.