Dallas, May 4 (NsNewsWire) — Two gunmen have been shot dead after they opened fire outside a conference on cartoons of the Prophet Muhammad in a suburb of Dallas, US police say.

A security guard was also injured. Police sealed off the Curtis Culwell Center in Garland and evacuated participants.

The event, organised by a group critical of Islam, was offering a cash prize for a drawing of the Prophet, reports BBC.

Dutch anti-Islamic politician Geert Wilders was among those attending.

He tweeted that shots had been fired and he had safely left the building.

It was not clear if the shootings were related to the event.

One eyewitness told the Associated Press news agency that he heard about 20 shots, which appeared to come from a car driving past the conference centre, followed by two individual shots.

The City of Garland government, in a statement on its Facebook page, said the security guard’s injuries were not life-threatening.

“As today’s Muhammad Art Exhibit event at the Curtis Culwell Center was coming to an end, two males drove up to the front of the building in a car,” it said.

“Both males were armed and began shooting at a Garland ISD (Independent School District) security officer. Garland Police officers engaged the gunmen, who were both shot and killed.”

It added that police suspect the gunmen’s vehicle could contain an “incendiary device” and a bomb squad was at the scene.

It said nearby businesses had been evacuated.

About 75 people inside the building were at first escorted to another room, US media reported. Later, a group of 48 were taken to a school bus and officials told attendees they would be taken to a nearby high school.

The BBC’s Alastair Leithead, in Los Angeles, says the event was controversial and provocative.

It was organised by the American Freedom Defence Initiative, which has campaigned against the building of an Islamic centre near the World Trade Center site in New York.

Sunday’s meeting included a $10,000 (£6,600) prize for a cartoon of the Prophet Muhammad.

The same conference centre in Garland hosted an event in January to raise funds for building a local Islamic centre; that meeting was picketed by opponents.

Depictions of the Prophet Muhammad are offensive to many Muslims.

There were widespread protests in 2006 when the Danish newspaper Jyllands-Posten published cartoons satirising the Prophet Muhammad.

In January this year, 12 people were murdered by two Islamist gunmen at the French magazine Charlie Hebdo, which had published similar cartoons.