French Prime Minister Jean-Marc Ayrault announced Saturday night that the terror alert Vigipirate plan was reinforced "immediately" for public transport, rallies and public buildings.

"The degree of vigilance Vigipirate remains, at this stage, in red. However, several measures are reinforced immediately," said the prime minister's office in a statement.

"These measures concern in particular public transport including rail and air, the safety of buildings open to the public and the safety of people's rallies," said the statement.

The decision was made shortly after President Francois Hollande announced in a television address after a defense council meeting that France will raise anti-terror alert to the highest level on fears of post-Mali operation reprisals after Paris' military commitment to help Malian authorities to stop Islamist rebels' offensive.

In accordance with the president's instructions, the prime minister had urged "all ministers concerned to implement these provisions without delay."

"The government is mobilized and remains attentive to the evolution of the situation. (It) shall take all necessary decisions to ensure national security," said the Matignon in the statement.

As French forces carried out air strikes for the second day on Saturday against Islamist rebels in Mali, the Jihadists warned that France's military intervention against them in northern Mali will put "not only for French hostages, but also for all French citizens wherever they find themselves in the Muslim world" at risk.

The Vigipirate plan, implemented in March 2003, has four levels: yellow, orange, red and scarlet, from the lowest to the highest. The level "reinforced red" is usually in force during sensitive periods such as Christmas and New Year.

The alert "scarlet" was briefly imposed in March 2012 in France's Midi-Pyrenees region at the time of the killings by Mohamed Merah in Toulouse and Montauban.

A major bomb explosion hit the Paris subway in 1995. It killed eight people and wounded 200 others.