Two brothers suspected of slaughtering 12 people in an Islamist attack on French satirical magazine Charlie Hebdo held one person hostage Friday as police cornered the gunmen northeast of the capital.

The hostage drama unfolded at a printing business in the small town of Dammartin-en-Goele, only 12 kilometres (seven miles) from Paris’s main Charles de Gaulle airport, police sources said.

Interior Minister Bernard Cazeneuve confirmed that an operation was under way to “neutralise” the suspects as the massive manhunt appeared to be reaching a dramatic climax with helicopters buzzing overhead and a huge deployment of security forces.

“An operation is under way which is set to neutralise the perpetrators of the cowardly attack carried out two days ago,” Cazeneuve said in a televised statement.

Police had already exchanged fire with the pair in a high-speed car chase. Prosecutors told AFP there had been “no casualties reported” in the immediate aftermath of the shoot-out.

Prior to the standoff, the suspects had hijacked a Peugeot 206 nearby from a woman who said she recognised them as the brothers, Cherif and Said Kouachi, accused of killing 12 people in Wednesday’s attack on the satirical weekly Charlie Hebdo, which repeatedly lampooned the Prophet Mohammed.

President Francois Hollande rushed to the interior meeting to be briefed on the situation as Prime Minister Manuel Valls declared that France was at “war” with terrorism, but “not in a war against religion.”

“It will without doubt be necessary to take measures” to respond to the terrorist “threat,” he said.

Two Air France planes were forced to abort their landing at Paris’s main Charles-de-Gaulle airport and go round again ‘due to the presence of helicopters… flying over the zone at low-altitude,” the airline said.

– ‘Mass casualty attacks’ –

The spectacular endgame came as it emerged the brothers had been on a US terror watch list “for years”.

And as fears spread in the wake of the attack, the head of Britain’s domestic spy agency MI5 warned that Islamist militants were planning other “mass casualty attacks against the West” and that intelligence services may be powerless to stop them.

Wednesday’s bloodbath at the satirical magazine Charlie Hebdo in Paris has sparked a global chorus of outrage, with impromptu and poignant rallies around the world in support of press freedom under the banner “jesuischarlie” (I am Charlie).

US President Barack Obama was the latest to sign a book of condolence in Washington with the message “Vive la France!” as thousands gathered in Paris on a day of national mourning Thursday, and the Eiffel Tower dimmed its lights to honour the dead.

And as a politically divided and crisis-hit France sought to pull together in the wake of the tragedy, the head of the country’s Muslim community — the largest in Europe — urged imams to condemn terrorism at Friday prayers.

In a highly unusual step, President Francois Hollande was due to meet far-right leader Marine Le Pen at the Elysee Palace later Friday, as France geared up for a “Republican march” on Sunday expected to draw hundreds of thousands.

– ‘Dressed like Robocops’ –

French authorities raised the security alert to the highest possible level in the region of Picardy, to the northeast of Paris, as forces tightened their noose on the brothers, Cherif Kouachi, 32 and Said, 34.

Around 24 hours into the manhunt, the brothers were identified after holding up a petrol station 80 kilometres (50 miles) from Paris.