Reports from Somalia suggest French commandos have carried out an operation to free a hostage, in which a number of people died.
Witnesses in Bulo Marer said they had heard helicopters above the southern town before explosions and gunfire.
Al-Shabab militants are believed to be holding a Frenchman hostage there.
An al-Shabab spokesman told AFP news agency “several” French soldiers had been killed, in a claim which could not be confirmed independently.
The office of Col Thierry Burkhard, the French military’s main spokesman for overseas operations, told AP news agency it had no information about any Somalia action.
The reported operation in eastern Africa came hours after France announced the start of a military intervention in the west African state of Mali, to support the government there against Islamist militants.
It was not immediately clear if the two events were connected.
A French secret agent named as Denis Allex was kidnapped in Somalia in July 2009 along with a colleague who was freed the following month.
‘Rescue bid’
A Somali intelligence official, speaking on condition of anonymity to AP, said French commandos had attacked the base in an apparent bid to rescue a foreign hostage.
Up to four helicopters were involved in the operation, witnesses say.
Mohamed Ali, a resident of Bulo Marer, described the events of Friday night by phone.
“We heard a series of explosions followed by gunfire just seconds after a helicopter flew over the town,” he told AP.
“We don’t know exactly what happened but the place was an al-Shabab base and checkpoint.”
Another resident of the town, Idris Youssouf, told AFP that details were sketchy because the attack had happened at night.
“But this morning we saw several corpses including that of a white man,” he added.
He said three civilians had also died in the fighting.
According to the website Somali Memo, which is broadly supportive of al-Shabab, militants fought off the French commandos.
Following the fighting, the situation in the town was calm and the militants had brought in reinforcements, the website said.
Hostage appeal
Mr Allex, reportedly an agent of France’s DGSE intelligence service, is one of nine French citizens currently held hostage in African countries.
Of the others, at least six are being held by the al-Qaeda in the Islamic Maghreb group, AFP reports.
Mr Allex appeared in a video in June 2010, appealing to France to drop its support for the Somali government.
He last appeared in another video in October, looking gaunt and calling on French President Francois Hollande to work for his release.
Somalia has not had an effective central government for more than two decades.
France has a large military base in neighbouring Djibouti, including army, marine and air force units.