Four foreign aid workers kidnapped at gunpoint in Kenya's Dadaab refugee camp have arrived back in Kenya's capital Nairobi aboard a military helicopter.

The workers - two men and two women from the Norwegian Refugee Council - were freed overnight after a short gunfight in southern Somalia where they were taken by their kidnappers.

"We are happy. We are back. We are alive and we are happy this has ended," Qurat-Ul-Ain Sadazai, one of the four workers with dual Canadian and Pakistani citizenship, said.

The other three hold Canadian, Norwegian and Philippine citizenship.

Elisabeth Rasmusson, the aid group's secretary general, told a news conference in Oslo, the Norwegian capital, that she was relieved the four had been released.

"What we know right now is that they have been released and are in good condition," she said.

Kenyan army spokesman Cyrus Oguna said: ""They are safe in our hands, they have been freed."

He said the workers, kidnapped on Friday, were released after a joint operation between Kenyan and Somali troops.

"They were released in a joint force of Somali and Kenyan forces, during which one of the kidnappers was killed," he said. Three others were arrested.

One has a bullet wound to the leg but they are otherwise unharmed.

"They are exhausted, they have walked far and have blisters, and one of the aid workers was shot in the leg, but otherwise they are in good health," Oguna said, adding they were now in the southern Somali border town of Dhobley.

"They are receiving medical attention at our base while they await transfer back to Kenya.

Mohamed Dini Adan, a Somali military commander in Dhobley, said the army had stopped the "kidnappers who were trying to hide and sneak past the army".

Somali forces heard reports that the gunmen were heading for a dense area of remote forest about 25km from Dhobley, and rushed to chase them down.

"Thanks to God we foiled their aims of taking the hostages into the forest," said Somali General Osmail Sahardid, who led the operation, adding that three of the gunmen had been captured.

Broad daylight

Al Jazeera's Nazanine Moshiri, reporting from Nairobi, said the group of kidnappers were on foot and had managed to get hold of a minibus, which then had two flat tyres.

"The Somali army in the area spotted these men, and followed them back to where they were holding the hostages. There was then an intense shoot out," she said.

"[The rescuing of the hostages] is good news for Kenya, as it was seen as highly embarrassing that the kidnapping took place in broad daylight in the refugee camp."

Residents in Dhobley said the local Ras Kamboni armed group, commanded by a former powerful Islamist warlord now allied to Kenya, were also involved in the rescue.

A Kenyan driver was killed and two others were wounded during Friday's attack.

Helicopters scrambled

Kenyan security forces scrambled military helicopters and aircraft after gunmen attacked the NRC convoy at around midday on Friday, while vehicles and troops on foot searched the remote scrubland either side of the porous border with Somalia.

However, the aid workers' vehicle, which the gunmen stole after killing the driver, was found abandoned a few hours after the attack, and fears grew the gang had escaped with the aid workers into Somalia.

Kenya, which invaded southern Somalia in October to attack al-Qaeda linked Islamist fighters, has troops about 120km deep into Somalia. However, the forces control only pockets of the vast territory.

The kidnapping was the latest in a series of attacks in Dadaab, where gunmen last October seized two Spaniards working for Medecins sans Frontieres (Doctors Without Borders).

They are still being held hostage in Somalia.

Source: Al Jazeera and Agencies