Armed police are surrounding a building where two men thought to be behind the Charlie Hebdo massacre are in hiding. Unconfirmed sources are saying the hostage is a man.
Links have also been made between the shooting of a female police officer yesterday in southern Paris and the terror attack at the magazine headquarters.
Twelve people were shot dead and 11 injured in the attack in the centre of Paris. Police are now in negotiation with the two suspects, brothers Said and Cherif Kouachi.
The suspected Islamists are reported to have said they are prepared to die.
In the UK, the head of MI5 has warned the threat of a terror attack is increasing.
Kim Sengupta, defence correspondent of the Independent, explains more.