Somali gunmen kidnapped three foreign aid workers on Saturday in a raid on a Kenyan border town, then went back over the porous border into the Horn of Africa nation, officials and residents said.
Cross-border raids are fairly common in the remote region, but usually involve cattle rustlers or gangs of robbers preying on business people in both countries. Ill-funded Kenyan security forces can do little to police the vast, impoverished area.
The militant al Shabaab group, which denied involvement in the attack, vowed to track down the kidnappers who took the aid workers from the town of Mandera which straddles the border between Kenya and Somalia.
"The authorities in Mandera (in Kenya) told us that those aid workers had been kidnapped. We're now going to run after them," said Sheikh Osman, an al Shabaab official in the neighbouring district in Somalia.
Another al Shabaab official said the captors were moving deeper inside Somalia.
"The kidnappers are in Somalia and heading to Bay and Bakol region. We informed our administrations there," said Sheikh Aden, the district commissioner.
No group has claimed responsibility for the attack.
The aid organisation has asked that its name and the nationalities not be released. In the past, most foreigners kidnapped have been released after a ransom payment.
Suspicion of kidnappings usually falls on clan militias or insurgents. Seizures inside Somalia happen often -- usually of Somalis, sometimes of foreigners and increasingly of ship crews off the coast.
On Tuesday, two French security officials were seized in the Somali capital Mogadishu and eventually handed over to al Qaeda-linked al Shabaab rebels.
Somalia's government and a 4,300-strong African Union force have been unable to wrest control of rebel strongholds in Mogadishu and other parts of the country despite international support and training.
A two-year insurgency there has killed at least 18,000 people, according to a local rights group.