A billboard for the controversial Oscars contender American Sniper has been removed after being daubed with the word "murder".

The red-painted graffiti appeared overnight on the advertisement in the Brentwood neighbourhood of Los Angeles.

The movie, which has been nominated for six Academy Awards including Best Picture, has prompted a nationwide debate since it opened across the country.

Its portrayal of the true story of former Navy SEAL Chris Kyle, credited with being the most lethal sniper in US military history, has been accused of glorifying violence.

Documentary-maker Michael Moore tweeted: "My uncle killed by sniper in WW2. We were taught snipers were cowards. Will shoot u in the back. Snipers aren't heroes."

Seth Rogen compared the movie to Nazi propaganda before adding that he liked it on Twitter.

The criticism prompted the former-vice presidential candidate Sarah Palin to mock what she called Hollywood leftists "caressing shiny plastic trophies".

She tweeted: "God bless our troops, especially our snipers."

The film, directed by Clint Eastwood and starring Bradley Cooper as Kyle, has broken the record for the highest grossing January release in history, raking in $100m last weekend.

The movie is based on Kyle's autobiography and tells the story of a career in which he recorded 160 confirmed 'kills'. It also relates his efforts to readjust to home life with his wife, played by Sienna Miller.

Kyle and a companion were shot and killed at a gun range in Texas in 2013.

They had gone there with the alleged gunman, a US Marine Corps veteran, to help him deal with his post-traumatic stress disorder.