Around a dozen suspects have been arrested over the killing of two French journalists in Mali, a police source in the north of the country told AFP on Monday.

Radio France Internationale (RFI) reporter Ghislaine Dupont, 57, and sound technician Claude Verlon, 55, were kidnapped and killed by what Foreign Minister Laurent Fabius said were "terrorist groups" in the flashpoint northeastern town of Kidal on Saturday.

"A dozen suspects have been arrested since the murder of two Radio France Internationale (RFI) journalists," said the source in Gao, the main city in northern Mali.

Their murder has shaken France, which just days ago was celebrating the return of four hostages who had been held for three years after being abducted in Mali's neighbour Niger.

Fabius told RTL radio on Monday "operations" were under way in Mali in a bid to "identify a certain number of people in camps".

But a source close to Defence Minister Jean-Yves Le Drian who refused to be named told AFP French forces had "information" that could allow the murderers to be tracked down.

Dupont and Verlon's bodies were found riddled with bullets just hours after they were kidnapped on Saturday, lying by a pick-up truck they had been abducted in.

Fabius said Dupont was killed with two bullets in the chest while Verlon "received three bullets in the head".

"When the French forces arrived behind the pick-up, they saw someone escaping not far away, around 1,500 metres (5,000 feet) away, they followed him but did not catch him."

The two veteran journalists had travelled to Kidal to interview a spokesman for the Tuareg separatist group the National Movement for the Liberation of Azawad (MNLA), and were abducted outside his home, according to their employer.

RFI quoted MNLA spokesman Ambery Ag Rhissa as saying he heard a commotion outside and saw the pair being bundled into a four wheel-drive vehicle after the interview.

Men in turbans and speaking the Tuareg language Tamashek "ordered Mr. Ag Rhissa to get back inside and forced the journalists' driver to lie down", RFI said, adding that Rhissa had heard Verlon and Dupont resist and protest.

A French military patrol found the victims' bodies lying near their car about 12 kilometres (seven miles) east of Kidal less than two hours after the kidnap, Fabius said.

The deaths come just three weeks ahead of parliamentary elections which are supposed to mark the completion of Mali's transition back to democracy following a military coup in March last year.

But there has been an upsurge in violence in the former French colony, where Paris sent troops early this year to drive out Islamists and Tuareg MNLA rebels who had seized the country's vast north after the coup.

The UN Security Council has strongly condemned the killings, while European Commission President Jose Manuel Barroso called them "barbaric".