By Jerome Cartillier with Eric Randolph in Paris
France and the US have pledged to step up the fight against the Islamic State (IS) group, urging Russia to throw its weight behind global efforts to resolve the four-year Syrian conflict.
President Francois Hollande met his US counterpart Barack Obama at the White House on Tuesday (local time) as Turkey's downing of a Russian warplane dealt a severe blow to efforts to co-ordinate the fight against IS.
Speaking 11 days after jihadists killed 130 people in the French capital, Hollande urged an "implacable" joint response to crush the group in Syria and Iraq.
At a joint press conference, Obama pledged America's full solidarity in the wake of the November 13 carnage, switching into Hollande's language to tell him, "We are all French."
Washington and Paris have both stepped up their fight against IS in Syria, with France launching its first strikes from the Charles de Gaulle aircraft carrier in the Mediterranean and the US calling for more international cooperation against the jihadists.
While announcing no specific new action, Hollande said he and Obama agreed to "scale up our strikes both in Syria and in Iraq to broaden our scope to strengthen our intelligence sharing regarding the targets."
Both leaders said they would boost support for forces battling IS on the ground, while continuing to rule out any ground campaign.
"France will not intervene militarily on the ground," Hollande said.
Illustrating the leaders' message on tighter cooperation, France said its warplanes had hit an IS command centre near its key western Iraqi stronghold of Mosul, in a strike led with the US Air Force.
Hollande and Obama reiterated their determination to see Assad step down in order to give Syria a chance for peace, with Hollande saying "it should be as soon as possible."
"He has been the problem – he cannot be the solution," Hollande said.
Hollande was in Washington as part of a frantic week of shuttle diplomacy as he tries to rally global support for increased strikes against IS, which claimed the Paris attacks.
Acting on a French resolution, the UN Security Council last week authorised "all necessary measures" to fight IS.
The French leader will hold talks in Paris with German Chancellor Angela Merkel on Wednesday and with Putin in Moscow on Thursday, before dining with Chinese President Xi Jinping in the French capital on Sunday.
But the diplomacy around the conflict was thrown brutally off course by the fighter jet downing, as Putin warned of "serious consequences for Russian-Turkish relations."
The US government has issued a worldwide travel alert warning American citizens of "increased terrorist threats" in the wake of Islamist attacks in Paris, Mali, Turkey and elsewhere.
But during a meeting with his national security team, Obama was briefed that there is "no specific, credible threat to the homeland from ISIL," the White House said.
Meanwhile, in Belgium, Brussels entered a fourth day of lockdown over fears of an "imminent" terror strike as the manhunt continued for the Belgian-born suspect Salah Abdeslam.
A fourth person was charged in Belgium in connection with the bloodshed in Paris.