The film has been condemned by several Muslim countries

Jaap de Hoop Scheffer's comments came after Afghans protested on Sunday against the film being made by far-right Dutch MP Geert Wilders.

The Dutch government has warned Mr Wilders that the film will damage Dutch political and economic interests.

Mr Wilders says the film is about the Koran but has given few details.

In the past, he has called for the Koran to be banned and likened it to Adolf Hitler's Mein Kampf.

The project has already been condemned by several Muslim countries, including Iran and Pakistan.

Nato's secretary general said he was concerned about his troops after the protests against the film in Afghanistan.

"If the [troops] find themselves in the line of fire because of the film, then I am worried about it and I am expressing that concern," he said in a television interview.

'Kick out forces'

On Sunday, hundreds of Afghans took to the streets in the northern city of Mazar-i-Sharif to protest against the film.

Demonstrators burned Dutch flags, and called for the withdrawal of Dutch troops from the Nato force.

The demonstrators say they will step up their protests unless the Afghan government expels the troops.

Mr Wilders is the leader of the Dutch Freedom Party

The protesters also criticised the recent republication of caricatures of the Prophet Mohammad in several Danish newspapers, and called for the withdrawal of Danish troops.

"We don't want our government to have any diplomatic relations with these two countries," Maulawi Abdul Hadi, one of the protesters, told the Associated Press news agency.

"We don't want Danish and Dutch troops in Afghanistan. They should be kicked out of the Nato forces here."

Mr Wilders has said he expects his 15-minute work will be shown in the Netherlands in March and released on the internet.

Dutch authorities have told him he may have to leave the country for his own safety amid reports of death threats.

Submission

Mr Wilders' film is called Fitna, an Arabic word used to describe strife or discord.

He has said his film will show how the Koran is "an inspiration for intolerance, murder and terror".

Mr Wilders leads the Freedom Party, which has nine seats in the Dutch parliament.

He has had police protection since Dutch director Theo Van Gogh was killed by a radical Islamist in 2004.

Van Gogh's film Submission included verses from the Koran shown against a naked female body.