Filmmaker Michael Moore has slammed snipers as 'cowards' who 'shoot you in the back' on the same weekend Oscar-tipped movie American Sniper hit cinemas.

Clint Eastwood's biopic of Navy SEAL Chris Kyle, starring Bradley Cooper, has become a box office hit since its release last week.

Taking to Twitter in rage, Fahrenheit 9/11 director Moore seethed: 'My uncle killed by sniper in WW2. We were taught snipers were cowards. Will shoot u in the back. Snipers aren't heroes. And invaders r worse.'

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Anger: Michael Moore took to Twitter with his views on snipers the day after American Sniper came out

American Sniper: The biopic of Navy SEAL Chris Kyle, starring Bradley Cooper, has become a box office hit since its release last week. Kyle was credited with the most confirmed kills in American military history: 160

Kyle was credited with saving hundreds of American lives by making 160 confirmed kills, which is the most in American military history. He claimed to have shot down 255.

The firm, which is based on Kyle’s autobiography of the same reveals not only how he became so successful, but also how the trauma of fighting in Iraq never left him.

Raised in rural Texas, Kyle started out as a cowboy and his initial application to join the SEALs was turned down because a rodeo accident had left him with metal pins in his arms.

However, in the late nineties, the unit relaxed its entrance policy and Kyle was put through the fearsomely tough selection and training regime.

In 2003, he was deployed to Iraq, where he made his first long-distance kills even though he had not been trained as sniper.

With an obvious talent, he was sent to the SEAL sniper school, where he was taught warfare’s loneliest and most controversial job.

Anti-guns: Moore (pictured) won an Oscar in 2002 for his documentary Bowling For Columbine, exploring gun violence in America and the main reasons for the Columbine High School massacre

True story: The movie is based on Kyle's autobiography, written before he was shot dead in February 2013

Oscar-tipped: Clint Eastwood's movie is hotly-tipped to pick up a few Oscars, including Best Actor for Cooper

In 2004, Kyle was posted to Fallujah, west of Baghdad and a major battleground of Iraqi insurgency, and it was during the battle for that city where he made his mark.

However, it was in 2006 in Ramadi, a city in central Iraq, that Kyle gained his nickname as ‘The Legend’ from his fellow SEALs.

One day, while positioned on a roof, Kyle watched a moped coming down a street. Riding it were two men, one of whom dropped a backpack into a pothole.

THE HIGHLY TRAINED MILITARY MARKSMEN A sniper is a highly trained military marksman, whose job is to engage targets from concealed postitions or from long distances. They usually operate alone or in small groups and use highly specialised weapons to take out their targets. It is believed the first use of snipers came during the American Revoluntionary War when colonists hid in trees and used early rifles to shoot British officers. The first unit of marksmen was established by the British army during the Napoleonic wars and the team were nicknamed the Green Jackets due to their distinctive green uniform. Snipers were widely used in the trenches during the First World War, with Germany equipping their fighters with scoped rifles, which could easily pick out targets. In the Second World War, British and French snipers were credited with halting the German advance. The longest recorded sniper kill was carried out by Corporal Criag Harrison of the British army's Household Cavalry when he two killed two Taliban machine gunners from more than a mile and a half away in Afghanistan in November 2009. He was using the British-built L115A3 Long Range Rifle, the Army's most powerful sniper weapon. Advertisement

Realising that it contained an improvised explosive, Kyle took a shot at the speeding moped from a range of 150 yards. The bullet hit one of the riders, passed through him, and hit the other.

In 2009, after four tours of Iraq, Kyle retired. He had not only shot more of the enemy than any other American sniper but had also gained himself a chestful of medals, including three Silver Stars for gallantry.

In February 2013 he was shot dead by a soldier he was trying to help who was suffering from severe post-traumatic stress.

The movie of Kyle's life is hotly tipped for glory at the Oscars, after being nominated for six awards including Best Actor for Cooper and Best Picture.

It has also been tipped for best adapted screenplay, sound mixing, film editing and sound editing.

Moore won an Oscar in 2002 for his documentary Bowling For Columbine, exploring gun violence in America and the main reasons for the Columbine High School massacre.

He is outspoken in his views against firearms and has previously described America's national symbol as the gun, not the bald eagle.

Last year Moore wrote on his Facebook page that that while other countries have more violent histories than the U.S., more guns per capita and consume the same violent movies and video games as the U.S., none have anywhere near the rates of mass killings that America does.

He explained: 'The bloodshed is just the latest in what is fast becoming a regular occurrence in the United States, and one that is sure to happen again, says Moore.

'We won't pass the necessary laws, but more importantly we won't consider why this happens here all the time,' he writes.