An armed man who holed up in a post office outside Paris has been arrested, police say, while two hostages he had taken have been freed.

Police had cordoned off an area near the post office in Colombes, a city north-west of Paris, during the incident.

Police said the incident did not appear to be linked with last week's jihadist attacks.

"There was no assault, the man gave himself up," a police source told AFP news agency, adding that the hostages were "shocked but not injured".

Police at Colombes, north-west of Paris. ( Twitter: Dario Spagnolo )

Photos on social media showed a helicopter and a large number of police cars at the scene.

Police sources earlier said the man was "speaking incoherently" and was heavily armed with grenades and Kalashnikovs.

An official at the city prosecutor's office confirmed an armed man had taken hostages.

"I cannot confirm or deny whether it is linked to terrorism," the official told Reuters, declining to give further details.

The French capital is still jittery after a series of attacks last week by Islamist gunmen left 17 people dead.

On Friday, police in Paris arrested a dozen people suspected of helping the militant gunmen behind the deadly assault on satirical newspaper Charlie Hebdo, the city prosecutor's office said.

The arrests came as United States secretary of state John Kerry visited Paris, expressing condolences on behalf of the US.

"I wanted to express to you personally, the sheer horror and revulsion that all Americans felt for the cowardly and despicable act, the assault on innocent lives and on fundamental values," he said.

"I really wanted to come here and share a hug with all of Paris and all of France."

Meanwhile, a French citizen allegedly linked to the Charlie Hebdo attackers who was arrested in Bulgaria on January 1 has denied being part of an Islamist group and is ready to be extradited to prove his innocence, his lawyer said.

French police officers in Colombes near the post office where the armed man was holed up. ( AFP: Kenzo Tribouillard )

AFP