Kenya will end its military campaign against the Islamist al Shabaab rebels in Somalia when it is satisfied it has stripped the group of its capacity to attack across the border, its head of military said on Saturday.

The east African nation moved its troops into Somalia in mid-October in pursuit of the Somali insurgents who it blames for a series of kidnappings on Kenyan soil and frequent assaults on its security forces in the border province of North Eastern.

A key success factor of this campaign will be in the form of a highly degraded al Shabaab capacity, Kenya's Chief of Defence Forces, General Julius Karangi told a news conference.

He said the government decided to move against al Shabaab in early October following near daily attacks on Kenyan forces on the border, and the kidnapping of two soldiers in July this year as well as Western tourists and aid workers.

Karangi rejected claims that the plan to go after al Shabaab had been planned carefully for many years with a view to annexing Somali territory to create a buffer zone between the two countries, with the help of Western nations.

When we feel as a country we are safe enough from this al Shabaab menace, we will come back where we belong, to our common border, Karangi said, adding there was no fixed deadline for the operation to end. We absolutely have no appetite for anybody's territory.

He confirmed that Kenya suffered its first casualty from combat on Friday when a soldier died from wounds after al Shabaab fighters ambushed a group of Kenyan troops. Emmanuel Chirchir, the military spokesman, tweeted that the dead soldier had been shot in the neck.

Fewer than five others have been injured in combat, Karangi said, adding that losses on the rebel side are conservatively estimated at several hundred dead.

Together with soldiers from the Transitional Federal Government of Somalia, the Kenyans have chased al Shabaab from the whole of Gedo region, Karangi said.

The military chief accused al Shabaab of recruiting impressionable Kenyan youths for radicalisation in Somalia, before deploying them to launch attacks on their own country.

GRENADE ATTACKS

Nairobi was stunned by two grenade attacks at a bar and a bus terminus that killed one person and wounded more than 20 on Monday, two days after the U.S. embassy had warned of an imminent threat in Kenya.

A Kenyan man pleaded guilty to one of the grenade attacks and membership of al Shabaab and was sentenced to life in prison by a Nairobi court. Two other Kenyan suspects are facing similar charges.

Kenyans have rallied around the government's move to take the war to al Shabaab, a group they see as a significant threat to the country's $35 billion a year economy.

The kidnapping of Western tourists has raised the threat of massive cancellations, ruining a tourism season that had been on track for a record year. Businesses have also complained of rising costs of shipping due to piracy off the coast of Somalia.

But the Kenyan public's resolve to support the military action is being tested by the attacks this week.

Four police officers drawn from the paramilitary General Service Unit were injured when a makeshift bomb went off on a road in northern Kenya as a convoy of police vehicles passed by.

That incident followed an attack on a vehicle carrying exam papers in the same province that killed four people on Thursday.

Kenya was surprised when Somali President Sheikh Sharif Ahmed cast doubts on his government's support for the incursion, just days after both states issued a joint communique endorsing the military action.

The Kenyan government requested an explanation of the remarks and a Somali delegation headed by the prime minister is expected in Nairobi on Sunday for further talks.