President Vladimir Putin ordered the Russian navy in the Mediterranean to establish contact with its French counterparts and work together "as allies" in a campaign against the Islamic State group in Syria.
A Facebook tool that let people check whether friends were safe after deadly attacks in Paris will be used more widely in the future, the social network said.
Britain should "think again" about taking part in air strikes on Islamic Statejihadists in Syria, Defence Secretary Michael Fallon said, after attacks in Paris that left at least 129 people dead.
Israel criticised "appallingly impudent" remarks by Sweden's foreign minister for drawing a parallel between the Paris attacks and the Palestinian-Israeli conflict.
President Francois Hollande said France would step up the battle against the Islamic State (IS) group in Syria in the wake of Paris attacks he dubbed "acts of war".
CIA director John Brennan warned that the attacks in Paris were likely not a "one off event" and that he expects the Islamic State group has more operations in the pipeline.
Blasts shook the Islamic State group's Syrian stronghold Raqa as French air strikes hit weapons depots and a training camp in response to the attacks in Paris.
French warplanes pounded Islamic State's Syrian stronghold in retaliation for a wave of coordinated attacks claimed by the jihadists which left 129 people dead in Paris.
Up to 20,000 people, among them Prime Minister Lars Lokke Rasmussen, gathered for a candlelight vigil at the gates of the French embassy in Copenhagen mourn the victims of the Paris attacks.
The defense ministers of France and the United States agreed on "concrete steps" to intensify cooperation against the Islamic State group, the Pentagon said.
German President Joachim Gauck said the world is confronted with a "new type of war" perpetrated by terrorists bent on killing those who refuse to follow their "barbaric ideology".
Multiple "terror" attacks in Paris increased the pressure on some 20 countries and organisations meeting in Vienna on Saturday to overcome deep divisions and help end Syria's horrific civil war.
Moscow called on Saturday for the international community to unite in its fight against terrorism after a string of attacks in Paris left more than 128 people dead on Friday.
The Paris attacks show it is more vital than ever to coordinate global efforts to fight terrorism, France's foreign minister said, vowing that French "international action" will not stop.