Lars Vilks, a Swedish cartoonist whose sketch of the Prophet Mohammad enraged many Muslims, was head-butted while giving a lecture about freedom of speech, he said.

Mr Vilks, who depicted the Prophet Mohammad with the body of a dog in 2007, said he was assaulted by a man sitting in the front row as he spoke at the University of Uppsala, about 70 kilometres from Stockholm.

"He head-butted me and I fell into the wall and lost my glasses," Mr Vilks was quoted by news agency TT as saying. He added he was unharmed.

A spokesman for Uppsala police said about 20 people tried to attack Mr Vilks after interrupting his lecture, adding that the police had to intervene to stop them. Two people were detained.

Mr Vilks was not immediately available to comment further. He says he has received death threats since his Prophet sketch.

In March an American who called herself Jihad Jane was charged with plotting to kill the Swede and using the internet to enlist co-conspirators.

In January, a Somali man was indicted for terrorism and attempted murder for breaking into the home of Danish cartoonist Kurt Westergaard and threatening him with an axe.

A cartoon by Mr Westergaard in 2005 which depicted the Prophet Mohammad with a turban shaped like a bomb sparked outrage across the Muslim world, with at least 50 people killed in riots in the Middle East, Africa and Asia.

Most Muslims consider any depiction of the founder of Islam as offensive.

- Reuters