Two pencils left with a note to pay tribute to the victims of a shooting by gunmen at the offices of weekly newspaper Charlie Hebdo in Paris, are seen outside the French embassy in London January 8, 2015. [Photo/Agencies]

LONDON - Britain has taken "precautionary" steps to increase security at the French-British border following the deadly attack on the Paris office of French magazine Charlie Hebdo, British Home Secretary Theresa May said Thursday.

Twelve people were murdered and 11 others injured when masked gunmen stormed the offices of the French satirical magazine in Paris on Wednesday.

Britain's international terrorism threat level remains at "severe," the second highest of all five possible threat levels, meaning that a terrorist attack is "highly likely" and the public should remain vigilant, May said in a statement.

"We have offered France every assistance necessary, including the full cooperation of our police and Security and Intelligence Agencies," she noted.

She added that the British officials were "in close contact with their French counterparts."

"The cowardly attacks that took place in Paris yesterday have shocked and sickened people in the United Kingdom and around the world. And they are a reminder of the very serious threat we face from terrorism," she deplored.

"In deliberately targeting and murdering journalists, the terrorists were attacking freedom and democracy. And in murdering police officers, they attacked the people who risk their own safety every day to protect us and our way of life," the home secretary continued.

On Thursday, May also chaired an emergency meeting to "consider Britain's response to the attacks and our own preparedness for a similar attack."

"I want to reiterate our commitment to standing with the French people against terror. The thoughts and prayers of all of us are with the families, friends and colleagues of the victims," she said.

In August last year, Britain upgraded its international terrorism threat level from "substantial" to "severe."