Ethnic Tuareg separatists are ready to support the French military intervention in Mali by taking on Islamist rebels on the ground in the north of the country, one of their senior officials told AFP on Monday.

"We're ready to help, we are already involved in the fight against terrorism," Moussa Ag Assarid, a representative of the Azawad National Liberation Movement (MNLA), said by telephone from northern Mali.

Islamists occupying northern Mali on Monday pushed further into the government-controlled south with an attack on the town of Diabaly, 400 kilometers (250 miles) north of the capital, as they have "retreated" in the east of Mali.

"The Islamists attacked the town of Diabaly today (Monday). They came from the Mauritanian border where they were bombed by the French army," said a Malian security source on condition of anonymity.

Islamists based in northern Mali, under daily bombardment by France's warplanes, vowed Monday to avenge the assault on French soil as well as in Africa.

"France has attacked Islam. We will strike at the heart of France," said Abou Dardar, a leader of Movement for Oneness and Jihad in West Africa (MUJAO), an offshoot of al-Qaida in the Islamic Maghreb (AQIM), speaking to Agence France Presse by telephone.

An emergency summit of leaders from west African bloc ECOWAS will meet in Abidjan on January 19, Ivorian Minister for African Integration Ally Coulibaly said Sunday, as the region readies troops to assist Mali in its fight against Islamists.

It was announced earlier in the day that the summit would take place on Wednesday. No reason was given for the postponement.

Germany's foreign minister on Sunday ruled out sending German troops to fight Islamists in Mali and called for a political solution to the violence as French forces joined attacks on the rebels.

Guido Westerwelle said he welcomed "the fact that the Malian army, with the support of France and African states, has managed to stop the Islamists' advance."

French jets pounded the Islamist strongholds of Gao and Kidal in northern Mali on Sunday, forcing insurgents to flee on the third day of a game-changing intervention that has been met with relief by the population and spurred the region into action.

"Stopping the terrorists -- it's done," French Foreign Minister Laurent Fabius said. "Today we started taking care of the terrorists' rear bases."

France has ordered tightened security, including anti-terrorist measures, following its military intervention against Islamists in Mali and Somalia, President Francois Hollande said Saturday.

Hollande said France "has to take all necessary precautions" in the face of a terrorist threat, including "surveillance of our public buildings and our transport network."

Around 60 Islamists including women in veils protested outside the French embassy in London on Saturday against France's military intervention in Mali.

The demonstrators held placards reading "French army, you will pay, the Muslims are on their way", "United Nations, go to hell" and "Sharia is the only solution for Mali".

British Prime Minister David Cameron on Saturday welcomed France's military intervention in Mali, saying he was deeply concerned about recent rebel advances.

Cameron also offered condolences to the families of a French hostage believed killed and two soldiers either killed or missing in a rescue attempt in Somalia and said it showed the need to fight terror in Africa.

Backed by French airpower, Mali on Friday unleashed an offensive against Islamist rebels who have seized control of the north of the country and were threatening to push south.

President Francois Hollande confirmed in Paris that French forces were supporting an attack aimed at repelling al-Qaida-linked radicals who have triggered international alarm this week with moves towards the capital Bamako.