Two gunmen who opened fire on a security officer outside a contest for cartoon depictions of the Prophet Mohammed have been shot dead in Texas.

The two gunmen were shot and killed by police outside the controversial event, which was being held in Garland, a suburb of Dallas, Texas.

Joe Harn of the Garland police department says a bomb squad is searching the vehicle outside the Curtis Culwell Centre as a "precaution".

He said police are not aware of any ongoing threat.

The gunmen have not been identified.

Mr Harn said it was not immediately clear whether the shooting was connected to the event inside, a contest awarding 10,000 dollars for the best cartoon depicting the Prophet Mohammed. 

Such drawings are deemed insulting to many followers of Islam and have sparked violence around the world.

According to mainstream Islamic tradition, any physical depiction of the Prophet Mohammed - even a respectful one - is considered blasphemous.

In January, 12 people were killed by gunmen in an attack against the Paris office of the satirical newspaper Charlie Hebdo, which had lampooned Islam and other religions and used depictions of Mohammed.

Pamela Geller, president of the AFDI, said she planned the event to make a stand for free speech in response to the outcries and violence over drawings of Mohammed.

Her group is known for mounting a campaign against the building of an Islamic centre close to the World Trade Centre site on New York City, and for buying advertising space in cities across the US criticising Islam.