Kenya sends in troops to Somalia in pursuit of al-Shabaab militants

Kenya has declared war on a Somali Islamist group and its army yesterday crossed into southern Somalia to pursue al-Shabaab, which it blames for a series of kidnappings inside its territory.

Kenyan tanks, troops, trucks and air support were seen inside its northern neighbour a day after the country's Internal Security Minister labelled al-Shabaab "the enemy" vowed to set up a "buffer zone" north of its border. There were also reports of US drone attacks on suspected militant training camps in Ras Kamboni, a coastal forest near the border with Kenya.

The biggest military action in Kenya's recent history comes five years after Ethiopia invaded Somalia with US approval and air support – an action that ended in ignominious withdrawal and helped to create al-Shabaab in its current form.

Kenyan forces entered an area of southern Somalia where they have previously been supporting at least two Somali militia groups fighting al-Shabaab for territory. However, Nairobi appears to have decided that its proxy war across the border was not working and has sent an occupation force instead.

The move could have drastic consequences for famine relief efforts as Kenya said yesterday that no more Somali famine refugees would be allowed to cross into camps in northern Kenya. Aid workers and UN staff around the Somali town of Dhobley, which has been the staging post for efforts to feed hundreds of thousands of starving people, were expected to be evacuated today.

Speaking on condition of anonymity, one senior aid official warned that the military operation "could backfire on humanitarian efforts".

Famine-blighted Somalia has been carved into warring enclaves over the past two decades and international attempts to deliver peace through backing individual factions have all ended in failure. "Ethiopia went in four years ago and made speedy progress to Mogadishu," said Roger Middleton, a regional analyst from the Chatham House think tank. "What they faced was an intense guerrilla war that drove them out and left behind a worse situation than before."

The military push follows the abduction in northern Kenya of four foreigners in the last two months by Somali gunmen. Al-Shabaab, which has lost territory during the Horn of Africa famine and is under pressure from African Union troops and rival militias in south and central Somalia, has not claimed responsibility for the kidnappings.

Al-Shabaab responded to Kenya's move yesterday by calling for a holy war: "Are you ready to live under Christians?" one al-Shabaab official shouted on a radio station in southern Somalia. "Get out of your homes and defend your dignity and religion. Today is the day to defend against the enemy."

The UN-backed transitional government, which controls the capital Mogadishu with the support of 9,000 African Union troops, said it was not consulted before Kenyan forces crossed the border.

"As a sovereign country we cannot condone any country crossing our border," Somalia's ambassador to Kenya, Mohamed Ali Nur, told The Independent yesterday. He also blamed al-Shabaab for the abductions but said that, while Kenya had the right to protect itself, it should do so within its own territory: "We will not allow any country to invade us."

East Africa's largest economy has been hit recently by the overflow from the crisis in its anarchic northern neighbour. The abductions of the British woman Judith Tebbutt and the French woman Marie Dedieu from holiday islands on the northern coast have affected tourism, which is an important foreign-currency earner.