Barack Obama meets with Francois Hollande at the Oval Office of the White House on Tuesday.

AFP/Washington

President Francois Hollande arrived at the White House on Tuesday seeking support for his newly declared war on the Islamic State group, as the US warned its citizens worldwide of heightened terror risks following the Paris attacks.

The French leader headed into hour-long talks with President Barack Obama on the campaign against IS in Syria and Iraq, as relations between Russia and Turkey - both key to resolving the Syria conflict - were plunged into crisis by Turkey's downing of a Russian warplane.

In Europe, the manhunt continued for Belgian-born Salah Abdeslam, a key suspect in the November 13 attacks that killed 130 people, while Brussels entered a fourth day of lockdown over fears of an "imminent" terror strike.

Police in France said they were analysing what is thought to be a suicide belt similar to those used in the Paris attacks, found without its detonator in a dustbin in the Montrouge suburb of the capital. Telephone data placed Abdeslam in the area the night of the attacks.

France's security crackdown since the attacks has seen police search more than 1,200 premises, arrested 165 people and seized 230 weapons - including "weapons of war" - Interior Minister Bernard Cazenueve said on Tuesday.

Authorities in neighbouring Belgium said they have charged a fourth person in connection with the bloodshed in Paris, which was claimed by the Islamic State group.

Brussels will stay on its highest level of alert at least until next Monday, with city-wide patrols of armed soldiers and police to ward off a threat the government said "remains serious and imminent," though schools and the Metro train system will re-open on Wednesday.

Shuttle diplomacy  

Hollande's trip to Washington is part of a frantic week of shuttle diplomacy by the French leader as he tries to rally global support for increased strikes against IS.

He will hold talks with German Chancellor Angela Merkel in Paris on Wednesday and with Putin in Moscow on Thursday, before dining with Chinese President Xi Jinping in the French capital on Sunday.

The UN Security Council last week authorised "all necessary measures" to fight IS.

But the delicate diplomacy around the conflict ran into further trouble after Russia confirmed one of its fighter jets had been shot down by Turkey at the Syrian border.

The US military backed up Turkey's claim that Turkish pilots had warned the Russian jet 10 times - but failed to get a response - before shooting it down.

But Russian President Vladimir Putin accused Ankara of "a stab in the back."

"Today's tragic event will have serious consequences for Russian-Turkish relations," he said.

Washington and Paris have stepped up their fight against IS in Syria, with France launching its first strikes from the Charles de Gaulle aircraft carrier in the Mediterranean on Monday and the US calling for more international cooperation against the jihadist group.

After a string of terror attacks in several countries, the US government issued a worldwide travel alert warning American citizens of "increased terrorist threats."

"Current information suggests that ISIL, Al-Qaeda, Boko Haram and other terrorist groups continue to plan terrorist attacks in multiple regions," said a State Department travel advisory.

Lockdown  

In Brussels, an eerie atmosphere hung over the city with soldiers in camouflage patrolling everywhere from railway stations to EU institutions.

France has said it will install security gates at stations in Paris and Lille for Thalys cross-Europe rail services by December 20.

A Thalys train from Amsterdam to Paris was attacked by a heavily armed man in August, but he was overpowered by passengers.

In Brussels' normally bustling historic Grand Place, a few bars and restaurants were open for business but they were struggling to find customers.

The only real activity downtown was deliverymen offloading crates for near-empty shops as builders hammered together stalls for a Christmas market meant to open on Friday.

"My grandson said we should up sticks and move to the south of the Yser river, just like in World War I (after the Germans invaded)," said Michel, a retired man from a Dutch-speaking suburb.

The European Union and Nato, which both have their headquarters in Brussels, said they would boost security and urged non-essential staff to work from home.

Meanwhile, the federal prosecutor's office announced that a man arrested in a police operation in Belgium late Sunday has been charged with involvement in the Paris attacks, the fourth so far.

Mohammed Amri, 27, and Hamza Attou, 20, were charged on Monday on suspicion of helping Abdeslam escape to Brussels after the attacks, while a third unnamed person faces charges of aiding him when he reached the city.

Abdeslam's brother Mohamed on Sunday told Belgian television he thought Salah had decided at the very last moment not to go through with his attack mission.