A freedom of expression contest for cartoon depictions of the Muslim prophet Muhammad was put on lockdown Sunday evening after a shooting outside the building. One security guard and two suspects were reportedly shot in the exchange.

The contest, held in a suburb of Dallas, Texas, was hosted by the American Freedom Defensive Initiative, partly in response to the Charlie Hebdo massacre by Islamic extremists in January for the magazine's depictions of Muhammad, something considered blasphemous by many Muslims. The "draw Muhammad" contest offered a $10,000 award for the best cartoon depicting the Muslim prophet.

The contest was disrupted when an officer in SWAT gear took the stage and told attendees and participants that they were being evacuated. The officer said two suspects and one officer had been shot.

AP reports that it is unclear if the shooting was related to the event and that the Garland Police Department spokesman declined to confirm officer's statement or provide details. Here's what AP knows thus far:

About 75 attendees were taken to another room. Later, a group of 48 people were escorted to a school bus. Authorities told attendees they would be taken to a nearby high school. A second group was set to be moved shortly after.

Johnny Roby of Oklahoma City, Oklahoma, was attending the conference. He told the AP he was outside the building when he heard around about 20 shots that appeared to be coming from the direction of a car passing by.

Police officers stand guard at an entrance as attendees are prevented from leaving the Muhammad Art …

Roby said he then heard two single shots.

He said he heard officers yell that they had the car before he was sent inside the building.

AP reports that AFDI did not immediately provide a response when emailed Sunday.

UPDATE: AP has confirmed that two men (whose identities have not been released) opened fire as the contest was letting out. The two men were shot dead by officers who were acting as security for the event. One security guard was shot in the leg and treated at a hospital:

The men drove up to the Culwell Event Center in North Garland, got out of their car and began shooting just as the "Muhammad Art Exhibit and Cartoon Contest" inside was coming to an end, Garland police spokesman Joe Harns said.

An unamed security guard was shot in the leg. He was later treated and released from a hospital.

Police who were helping with security at the event fired back, killing both gunmen, Harns said. [...]

FBI and local officials were checking on the gunmen's vehicle for explosives, a law enforcement official told CNN. The area around the center was blocked off.

Image via AP.