Hollande meets Obama to ramp up fight against IS

French President Francois Hollande flies into Washington on Tuesday seeking support for his newly declared war on the Islamic State group after the Paris attacks, while the United States announced a worldwide travel alert for its citizens.

Back in Europe, the manhunt continued for Belgian-born Salah Abdeslam, a key suspect in the Paris attacks that killed 130 people, while Brussels entered a fourth day of lockdown amid fears of an "imminent" attack.

French police said they were analysing a suspected 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 on the night of 13 November.

Brussels will stay on its highest level of alert at least until next Monday, with Belgian Prime Minister Charles Michel warning that the threat "remains serious and imminent", though schools and the Metro will reopen Wednesday.

The security measures include the patrols citywide of armed soldiers and police, something a counter-terrorism expert says has not seen in at least two decades.

Belgian authorities have charged a fourth person in connection with the bloodshed in Paris, which was claimed by the Islamic State group.

Shuttle diplomacy

Washington and Paris have stepped up their fight against IS, with France launching its first strikes from an aircraft carrier in the Mediterranean and the United States calling for more international cooperation against the extremistt group.

Underlining heightened global fears of attacks after Islamists killed scores in Mali, Turkey, Lebanon and Nigeria in recent weeks, the US government issued a worldwide travel alert warning American citizens of "increased terrorist threats".

"Current information suggests that ISIL (another acronym for Islamic State), al-Qaeda, Boko Haram and other terrorist groups continue to plan terrorist attacks in multiple regions," said a State Department travel advisory.

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 Russian President Vladimir Putin in Moscow on Thursday, before receiving Chinese Premier Xi Jinping in the French capital on Sunday.

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

Lockdown

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

The army and armed police will remain on the streets in coming days, the Belgian prime minister said, but schools and the metro system would reopen from Wednesday.

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

The alert will be reviewed again on Monday.

Meanwhile the federal prosecutor's office announced that a man who was arrested during 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.