NAIROBI, Kenya - Two French security advisers being held hostage in Somalia will soon be tried under Islamic law for alleged spying and "conspiracy against Islam," a senior member of a rebel group holding the men said Saturday.

The official with the insurgent group al-Shabab said no date had been set for the trial. He asked that his name not be published because he is not authorized to speak to the media on the matter.

The Shabab has been criticized for its severe forms of punishment, including public executions, stonings and amputations.

The French men were abducted Tuesday from a hotel in Mogadishu, the capital of Somalia. They were in the country to train Somali government forces, which are fighting Islamist militiamen.

Foreigners rarely travel to Somalia, which is among the most dangerous countries in the world.

On Saturday, a security official said gunmen seized three foreign aid workers in northern Kenya and took them across the border into Somalia.

Roughly 10 gunmen arrived late Friday night at a house in the border town of Mandera where the workers were staying, shot the watchman in the head and kidnapped the three workers, the official said, speaking anonymously because he was not authorized to talk to the media.

He would not say who the victims worked for or what their nationalities are.

The watchman was hospitalized with life-threatening injuries, the official said.

Somalia has not had a functioning government for 18 years since clan warlords overthrew a brutal socialist dictator then unleashed their militias on each other.

Kidnappings for ransom have been on the rise in recent years, with journalists and aid workers often targeted. The lawlessness also has allowed piracy to flourish off the coast, making the waterway one of the most dangerous in the world.

Many fear the power vacuum in Somalia will provide a haven for terrorists, as the military and police force are weak and in disarray. Various Islamist groups have been fighting the U.N.-backed government since being chased from power 2 1/2 years ago. The situation is complicated by the continual splintering and reforming of alliances and a web of clan loyalties.

Somalia's capital, Mogadishu, sees near daily battles between government and insurgent forces. Tens of thousands of civilians have been killed.