US troops killed by Iraqi soldier
Two US troops have been killed by an Iraqi soldier who apparently smuggled real bullets into a training exercise and opened fire.
The incident raises fresh concerns about the nation's security forces as the Americans prepare to leave by the end of this year.
A US military official said the gunman was immediately killed by American soldiers who were running the morning drill at a training centre on a US base in the northern city of Mosul.
He said the exercise was not meant to involve live ammunition, and an Iraqi army officer said the shooting appeared to have been planned.
A US statement confirmed that two soldiers were killed and a third was wounded by small-arms fire by what the military described as "an individual wearing an Iraqi army uniform".
Meanwhile, another American soldier was killed on Saturday during an unrelated military operation in central Iraq - making it one of the deadliest days for US forces in the country in months.
The Mosul attack underscores the threats that US forces continue to face in Iraq even though most of the estimated 47,000 troops no longer go on regular combat missions.
The vast majority of American troops left - down from nearly 170,000 in 2008 - are all but confined to bases where they help train Iraqi police, soldiers and pilots how to protect the country from threats like insurgents and invasions.