Gun attacks north of Baghdad killed seven members of Iraq's security forces Tuesday, the latest in a surge in violence fuelling fears the country is slipping back into all-out conflict.

Coupled with a deadly standoff between security forces and anti-government fighters in the western province of Anbar, unrest this month has left more than 850 people dead, the worst prolonged period of bloodshed since Iraq began emerging from a brutal sectarian war in 2008.

On Monday the United States said it plans to sell Iraq 24 Apache attack helicopters in a $4.8 billion deal to help the country fight militants while foreign leaders have urged the Shiite-led government to address long-term grievances in the disaffected Sunni community to undercut support for militancy.

In Tuesday's deadliest violence, five soldiers and one Sahwa anti-Qaeda militiaman were killed in a gun attack on their joint checkpoint near the restive city of Baquba, north of Baghdad, security and medical officials said.

The shooting comes a day after two policemen and a Sahwa fighter were shot dead and then decapitated near Samarra, also north of the capital.

The Sahwa are a collection of Sunni Arab tribal militias that moved against their co-religionists in Al-Qaeda and joined with the US military from late 2006 onwards, helping turn the tide of Iraq's insurgency.

Sunni militants regard them as traitors and often target them, as well as Iraq's security forces.

Also on Tuesday, a police intelligence officer was kidnapped and killed with a single gunshot to the head in the northern city of Kirkuk, a security officer and a doctor said. The body bore signs of torture.

More than 850 people have been killed so far this month as a result of violence in Iraq, more than three times the toll for January 2013, according to an AFP tally.

It comes as security forces are locked in battles with militants, including those affiliated with the Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL), in Anbar, a mostly-Sunni desert region west of Baghdad that shares a border with Syria.

The standoff has forced more than 140,000 people to flee their homes, the UN refugee agency said, describing this as the worst displacement in Iraq since the 2006-2008 sectarian conflict.