The US has issued a worldwide travel alert to its citizens, citing terrorist threats from Isis, al-Qaeda, Boko Haram and "other terrorist groups".
The alert from the US State Department urges US citizens to exercise caution in public places and during holidays and public events.
French President Francois Hollande will meet Barack Obama at the White House on Tuesday to discuss the fight against so-called Islamic State.
Militants who attack civilians around the world suffer from an "intellectual and psychological disease" and use religion as a front, Egypt's most senior Muslim cleric has declared.
Sheikh Ahmed al-Tayeb, the head of the al-Azhar centre of Islamic learning in Egypt, condemned the recent bloodshed in Paris, Mali and elsewhere committed under the banner of Islam during a meeting of the Muslim Council of Elders.
He said the violence had "no link" to authentic Islam. Terrorism was a "life philosophy", he said, but was not the by-product of any of the Abrahamic faiths, which include Judaism and Christianity.
France and the US have agreed to step up airstrikes in Syria and Iraq to target IS in the wake of the Paris attacks.
Britain will do "all in our power" to support France in the fight against IS following the Paris terror attacks, David Cameron said.
The United Nations Security Council agreeS to intensify efforts to 'eradicate' Islamic State in the wake of the Paris terror attacks.