French police have surrounded a building in a northern town where two men suspected of the Charlie Hebdo massacre are said to have a hostage.
Shots have been fired and several people are said to have been wounded in Dammartin-en-Goele, 35km (22 miles) from Paris.
The development comes nearly 48 hours after the attack on the magazine's office, when 12 people were shot dead.
The heavily armed gunmen fled Paris by car after the attack.
The attackers, who shouted Islamist slogans, are believed to have been angered by the satirical magazine's irreverent depictions of the Prophet Muhammad.
They are said to have shouted "We are al-Qaeda, Yemen", an apparent reference to the al-Qaeda in the Arabian Peninsula group (AQAP).
In the US, a senior official has told reporters that one of the two brothers alleged to have carried out the attack, Said Kouachi, spent "a few months" training in Yemen with the group.
Said and his younger brother, convicted terrorist Cherif Kouachi, were on a US no-fly list before the attack, a US counter-terrorism official told the New York Times.At the scene: Piers Scholfield, BBC News, Dammartin-en-Goele
It's a dramatic scene. The area around the small town of Dammartin is rapidly filling up with thousands of French police and anti-terror forces.
Several Puma helicopters are hovering over the area. Hundreds of police cars and armoured vehicles have arrived. Press were rapidly moved on from the area amid warnings of danger to onlookers.
Huge convoys of police line the main N2 highway.
There are now reports of flights being cancelled at nearby Charles de Gaulle airport.Residents warned
In Dammartin, witnesses say police are protecting people in buildings close to the siege of a printing firm building.
Officers from the elite GIGN unit have told people working nearby to stay inside and turn lights off while the operation is going on.
People in the area say police helicopters began arriving around 08:45 (07:45 GMT) followed by convoys of armed officers.
Some of those in premises in the industrial area where the suspects are cornered have been evacuated.
Police and military helicopters continue to hover low over the area, while lines of armed officers are guarding the edge of the national highway were traffic continues to flow.
The security situation at the town of Dammartin-en-Goele has affected flights at the main airport in Paris, which is in the vicinity. Officials at Paris Charles de Gaulle say they have changed landing and take-off patterns for aircraft in the light of the security situation.
Meanwhile, police are said to have have identified a suspect in Thursday's fatal shooting of a policewoman in Montrouge, south of Paris.
AFP news agency quotes a source close to the investigation as saying that two people in his immediate circle have been taken into custody.Charlie Hebdo victims
- Economist and regular magazine columnist Bernard Maris, 68, known to readers as "Uncle Bernard"
- Cartoonists Georges Wolinski, 80, and Jean "Cabu" Cabut, 76
- Charlie Hebdo editor and cartoonist Stephane "Charb" Charbonnier, 47, who had been living under police protection since receiving death threats
- Cartoonists Bernard "Tignous" Verlhac, 57, and Philippe Honore, 73
- Mustapha Ourrad, proof-reader
- Elsa Cayat, psychoanalyst and columnist, the only woman killed
- Michel Renaud, who was visiting from the city of Clermont-Ferrand
- Frederic Boisseau, 42, caretaker, who was in the reception area at the time of the attack
- Police officers Franck Brinsolaro, who acted as Charb's bodyguard, and Ahmed Merabet, 42, who was shot dead while on the ground
On Thursday, France marked a national day of mourning for those killed in Paris.
A minute's silence was held in public spaces and 20 imams joined hundreds gathered outside the offices of Charlie Hebdo to express sympathy for the victims. Later, the lights on the Eiffel Tower were turned off as a mark of respect.
Several thousand people gathered in the Place de la Republique in Paris for a second night, lighting candles and waving signs that read "Je suis Charlie" ("I am Charlie"). Other vigils were held across the world
The lawyer for Charlie Hebdo, Richard Malka, has said that next week's edition of the magazine will go ahead on Wednesday and will have a print run of one million instead of the normal 60,000 copies.
Politicians and journalists across the globe have widely condemned the shooting as an attack on freedom of speech and the press.