Attacks across Iraq killed 16 people on Sunday, while new figures showed violence last month claimed more than 900 lives as the country grapples with its worst bloodshed in years.

Data compiled separately by the United Nations and the Iraqi defence, interior and health ministries showed that unrest was near its worst since 2008, when it was slowly emerging from a brutal Sunni-Shiite sectarian war.

The latest bloodletting comes as political leaders jostle to build alliances during what is expected to be a protracted period of government formation following April elections.

The worst of Sunday's violence targeted security forces north of Baghdad, in the restive provinces of Salaheddin, Diyala and Nineveh.

In the single deadliest attack, five off-duty soldiers riding a taxi between Baiji and Samarra, in Salaheddin, were ambushed by militants who freed the vehicle's driver but proceeded to kill all the soldiers.

Elsewhere in the province, three soldiers and a policeman were killed in separate roadside bombs.

In the main northern city of Mosul and surrounding Nineveh province, four others died in a series of shootings and bombings, while a policeman was killed in Muqdadiyah, Diyala province.

Two teachers were also shot dead in Baghdad, officials said.

No group immediately claimed responsibility for the violence, but Sunni militants, including those linked to the Islamic State of Iraq and the Levant jihadist group, frequently target the security forces, ostensibly in a bid to destabilise Iraq and undermine public confidence in them.

- 'Sustained violence' -

The violence came as new figures were published Sunday showing violence is near its highest in years.

According to the UN's mission to Iraq, at least 799 Iraqis were killed in "acts of terrorism" and other violence, while a further 195 died as a result of military operations in the conflict-hit province of Anbar, in western Iraq.

Separate figures released by Iraqi ministries, meanwhile, put the toll at 938 killed, including 804 civilians, and 1,463 wounded.

"I strongly deplore the sustained level of violence ... that continues rocking the country," UN special envoy Nickolay Mladenov said in a statement.

"I urge the political leaders to work swiftly for the formation of an inclusive government within the constitutionally mandated timeframe and focus on a substantive solution to the situation in Anbar."

The month's deadliest bloodshed struck on May 28, when 78 people were killed in a series of attacks nationwide, the bloodiest of which hit Baghdad and Mosul.

Iraqis have been targeted by shootings, roadside bombs, suicide attacks and vehicles rigged with explosives.

Over the past months, violence has targeted civilians, civil servants and security forces alike, and hit cafes, restaurants, markets and football pitches, along with checkpoints and official buildings.

Anti-government fighters have also maintained control of Fallujah, a city just west of Baghdad, and shifting parts of nearby Ramadi, capital of Anbar province, since the beginning of the year.

Iraqi officials blame external factors for the rise in bloodshed, particularly the civil war in neighbouring Syria, and insist that wide-ranging operations against militants, particularly in Anbar, are having an impact.

But the bloodletting has continued unabated, while analysts and diplomats insist the Shiite-led government must do more to reach out to the disaffected Sunni minority in order to undermine support for militancy.