Kenyan security forces searched border regions with Somalia in the hunt for armed kidnappers who seized four aid workers from Dadaab, the world's largest refugee camp.
The two men and two women who work with the Norwegian Refugee Council (NRC), come from Canada, Norway, Pakistan and the Philippines.
A Kenyan driver was killed and two others were wounded during yesterday's attack.
Aerial searches were ongoing using both military helicopters and aircraft, while vehicles and troops on foot searched the remote scrubland either side of the Somalian border.
Kenya has troops 120km deep into Somalia. However, the forces control only pockets of the vast territory.
But despite fears the gunmen and their hostages would head for Somalia - around 100km from Dadaab - a Kenyan security force spokesman said he was hopeful they remained inside Kenya.
The aid workers' vehicle, which the gunmen stole after killing the driver, was found abandoned a few hours after the attack.
NRC is working to support some 465,000 inhabitants in the Dadaab complex, which constitutes Kenya's third-biggest town in terms of population.
The kidnapping is the latest in a series of attacks in Dadaab, where gunmen last October seized two Spaniards working for Medecins sans Frontieres. They are still being held hostage in Somalia.
Kenya has voiced concern that Dadaab too poses a security threat, and has blocked registration of new refugees to the camp.
