Traditionally hostile to foreign interference, Algiers has thrown its support behind operations in Mali against Islamist forces in a surprise about-turn that saw it open its skies to French warplanes.

But some observers say Algeria's change of heart followed a "betrayal" by armed rebel groups in Mali who vowed to cease hostilities last month, and represents a failure of its non-interventionist policy.

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.

Demonstrators blocked the road outside the French embassy in Beirut on Monday after a French court postponed the release of Lebanese leftist militant George Abdallah, who has spent 28 years in jail, as Prime Minister Najib Miqati condemned the “unjustified” delay.

Dozens of leftist protesters and supporters of Abdallah rallied in front of Paris' embassy in the Mathaf area, condemning the policies of France and accusing it of being a proxy for the United States, which has openly rejected the release of the Lebanese activist.

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.

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".

Turkish Prime Minister Recep Tayyip Erdogan called on France on Saturday to "immediately" clarify the killing of three Kurdish activists who were shot dead in Paris, while asking French President Francois Hollande to explain why he was meeting with members of the outlawed PKK.

"France must immediately clarify this incident," Erdogan said in televised remarks. "Also, the French head of state must explain immediately to the French, Turkish and world public why ... he is in communication with these terrorists," he added.