The French satirical weekly Charlie Hebdo, targeted in a deadly attack earlier this year by Islamist gunmen, was honored on Tuesday at a New York gala under heavy security, organizers said.

The award from the PEN American Center came two days after two gunmen opened fire at a Texas exhibit of caricatures of the Prophet Mohammad, depictions that Muslims consider offensive.

Drawings of the founder of Islam were also at the heart of the January attack on Charlie Hebdo's Paris offices that killed 12 people. Al Qaeda's branch in Yemen claimed responsibility, saying the weekly's cartoons had insulted the Prophet.

"Charlie Hebdo's current staff have persisted, and tonight's award reflects their refusal to accept the curtailment of lawful speech through violence," PEN President Andrew Solomon told the gala, filled with literary figures.

Accepting the award, Charlie Hebdo's editor-in-chief Gerard Biard said the most powerful weapon of religious extremists is fear and "we must disarm them."

"They don't want us to write and draw. We must write and draw," he said. "They don't want us to think and laugh. We must think and laugh. They don't want us to debate. We must debate.

"Being here tonight, we contribute to disarming them," he said.

PEN's decision to give the Freedom of Expression Courage Award to Charlie Hebdo prompted six prominent writers to withdraw from the event, said PEN, an organization advocating on behalf of writers persecuted because of their work.

One novelist who withdrew, Rachel Kushner, said she was not comfortable with Charlie Hebdo's "cultural intolerance," PEN said.

Uniformed officers, counterterrorism units and police dogs were visible around the American Museum of Natural History, where the event was held.

Speaking outside, New York Police Department Deputy Commissioner of Intelligence and Counterterrorism John Miller said there had been calls on social media for further violence since the Texas attack, which left the two gunmen dead.

"Some of it is literally just that, chatter. But as we saw in Texas, some of it is indicative," he said.

Charlie Hebdo was being honored "for the same things that brought that attack on in a very public venue in the heart of New York City," Miller said.

"If you factored that, plus the events in Texas the other day where violence stirring around the same issue happened, and there are calls on social media for more violence around that issue against the same targets, this becomes a very obvious place to have a lot of protection," he said.