A series of attacks in Baghdad and Sunni Arab areas north of the capital killed nine people on Monday, as Iraq grapples with a months-long surge in nationwide violence.

Coupled with a protracted stand-off between security forces and anti-government fighters in the western province of Anbar, unrest this month has left more than 850 people dead, fuelling fears Iraq is slipping back into the brutal conflict that plagued it in 2006-2007.

Foreign leaders and diplomats have urged Iraq's Shiite-led government to address long-term grievances in the disaffected Sunni community to undercut support for militants, but with elections due in April, Prime Minister Nuri-al-Maliki has taken a hard line.

Attacks on Monday struck in Baghdad, and in and around the restive mostly-Sunni cities of Baquba, Mosul and Samarra, security and medical officials said.

In the most brutal incident, gunmen killed two policemen and an anti-Qaeda Sahwa militiaman in an attack on their joint checkpoint near Samarra and then decapitated them.

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, in attacks.

Elsewhere, gunmen killed three people, including a police officer, in separate shootings in Baghdad, while two policemen were gunned down in the main northern city of Mosul.

Mortar fire in Muqdadiyah, near Baquba in confessionally-mixed Diyala province, killed one person and wounded three others.

The latest bloodshed took the overall death toll for the month above 870 -- 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.