Aid workers kidnapped from Kenya's Dadaab camp near Somalia

Dadaab refugee camp in Kenya is home to more than 450,000 Somalis

A Kenyan driver has been killed and four foreign aid workers kidnapped at a refugee camp in Kenya close to the border with Somalia, police say.

The foreigners, from Canada, Norway, Pakistan and the Philippines, worked for the Norwegian Refugee Council.

They were travelling in a convoy when they were ambushed by gunmen in Dadaab, which houses more than 450,000 Somalis.

Several aid workers have been kidnapped from Dadaab in the last year and many groups have withdrawn from the camp.

'Helicopter search'

The region's deputy police chief, Philip Ndolo, said two vehicles in the convoy had come under attack - and one had managed to get away.

He told the AFP news agency that the driver of the second vehicle was shot by a gunman and died while receiving treatment at hospital, correcting earlier reports that he had also been kidnapped.

Two other Kenyans were also shot, another driver and a contractor for the Norwegian Refugee Council, Reuters news agency reports Mr Ndolo as saying.

A spokesman for the Norwegian Refugee Council said its secretary general, Elizabeth Rasmussen, was in the convoy that came under attack, but she had escaped unharmed.

Somalia has had no effective central government since 1991, and has been wracked by fighting ever since - a situation that has allowed piracy and lawlessness to flourish.

Islamists from the al-Qaeda-linked group al-Shabab control large swathes of the country.

"We suspect this could be the work of al-Shabab sympathisers," Mr Ndolo told Reuters.

Kenyan army spokesman Cyrus Oguna told AFP that the seized vehicle had been found abandoned about 30km (18 miles) from Daadab and it was believed the captives and their abductors were still inside Kenya, proceeding on foot.

"We have dispatched military helicopters to pursue the kidnappers," he said.

Last October, Kenyan troops entered Somalia in pursuit of al-Shabab militants accused of being behind various kidnappings on Kenyan soil and of destabilising the border region.

Earlier that month, two Spanish doctors working for the medical charity Medecins Sans Frontieres were kidnapped from Dadaab and are still being held hostage.