French President Francois Hollande has said his country will intensify air strikes against Islamic State (IS) militants in Syria and Iraq.
Speaking in Paris after talks with UK PM David Cameron, Mr Hollande confirmed French aircraft carrier Charles de Gaulle would join the military action.
It comes as the Belgian capital, Brussels, remains on the highest level of terror alert for a third day.
Suspected Paris attacks gunman Salah Abdeslam remains at large.
The two leaders agreed to step up co-operation on countering international terrorism, including increased data-sharing and sharing of airline records.
The Islamic State group has said it was responsible for the Paris attacks, in which 130 people were killed.
“I firmly support the decisive action taken by President Hollande to strike Isil [IS] in Syria, it is my firm belief that we should do so too,” Mr Cameron said in a statement at a news conference.
Mr Hollande said: “We will intensify our strikes, choosing targets that will do the most damage possible to this army of terrorists.”
In Brussels, the federal prosecutor’s spokesman said five people had been arrested following a police operation on Sunday night in the Brussels region and in the Liege region.
These arrests bring to 21 the number of people arrested as part of Belgium’s ongoing terror alert.
This is just the start of Mr Hollande’s week of diplomacy. The emphasis in each meeting will be slightly different. Aside from the need to assess the US-led military strategy in the Middle East, there are growing calls from European leaders to improve intelligence- and data-sharing.