Paris (AFP) - French President Francois Hollande said Tuesday's attacks in Brussels that killed at least 26 people struck at "the whole of Europe".
"Through the attacks in Brussels, the whole of Europe has been hit," Hollande said in a statement, urging the continent to take "vital steps in the face of the seriousness of the threat".
French Prime Minister Manuel Valls said: "We are at war. Over the past few months in Europe, we have endured several acts of war."
France, which neighbours Belgium to the south, was hit by two major terror attacks in 2015 and several of the jihadists involved came from Brussels.
The November 13 attacks in Paris claimed 130 lives, 10 months after attacks on the satirical newspaper Charlie Hebdo and a Jewish supermarket left 17 dead.
The last surviving jihadist of a 10-man team who carried out the November attack, Salah Abdeslam, was arrested in Belgium on Friday, where the attackers had rear bases and what appears to be an extensive network of support.
Speaking on Sunday, Belgian Foreign Minister Didier Reynders said Abdeslam told investigators "he was ready to restart something in Brussels".
Following Tuesday's bloodshed in Brussels, Hollande spoke with Belgium's Prime Minister Charles Michel, and the two exchanged "information, intelligence" and discussed "questions of police and security cooperation," his office said.
French Interior Minister Bernard Cazeneuve earlier announced that Paris was deploying 1,600 additional police to border crossings and air, sea and rail infrastructure after the Brussels attacks.
Germany and the Netherlands also announced stepped up security measures at borders, airports and rail stations.