A suicide bomber in Baghdad left five dead as they queued for fuel

In the bloodiest single incident, 13 Iraqi soldiers died when a suicide attacker drove a fuel tanker into an army base in Mosul in northern Iraq.

The US military said it killed 12 militants preparing suicide attacks in a house east of Baquba.

At least 15 people died in rocket and mortar fire apparently aimed at Baghdad's Green Zone.

Eight were civilians who were killed when rockets landed short of their targets on Sunday morning.

The bloodshed comes despite an overall reduction in violence since last June.

That was when the US deployed an extra 30,000 troops in violence-hit areas - the so-called "troop surge".

But Sunday's violence underlines the fragile, reversible nature of the apparent improvements in security, say correspondents.

Huge blast

At least 40 people were injured in Sunday's early-morning suicide strike in Mosul.

Sunday also saw a barrage of fire hit Baghdad's Green Zone

The suicide attacker ploughed an explosives-laden tanker into the army base, causing a massive blast.

Iraqi and US soldiers have been engaged in a major offensive in Mosul, which US commanders say is al-Qaeda's last urban stronghold in Iraq.

In another deadly attack, at least seven shoppers in a Baghdad market were killed when gunmen travelling in three cars opened fire.

At least 16 people were wounded when the drive-by shooting happened in the southern Zaafariniya area of the city, police said. The gunmen fled the scene.

In other violence:

at least five people were killed when a suicide bomber struck a queue outside a petrol station in the Shula district of Baghdad, police said

a roadside bomb killed five Iraqi soldiers close to the city of Kirkuk - the scene of growing sectarian strife

at least three people were killed when a suicide car bomb was driven into the house of a tribal leader near Samara

Bodies 'shaved'

The attacks on the Green Zone - which began at about 0600 (0300 GMT) - set the warlike tone of the day.

The first rocket barrage sounded like successive peals of thunder. It left a shroud of stinking black smoke over the city, reports the BBC's Adam Brookes.

Some relatives were mourning those struck by a stray rocket

A second barrage followed about four hours later, leaving four wounded. A third attack followed four hours after that. Iraqi police told the BBC that seven people died in the latest attack.

Our correspondent says previous rocket attacks on the Green Zone have been blamed on rogue elements of Moqtada Sadr's Mehdi Army militia, which is supposed to be observing a ceasefire.

Also on Sunday, the US military said it had killed 12 men in a raid east of Baquba city, in Diyala province.

Spokesman Major Winfield Danielson claimed six of the men killed were found to have shaved their bodies, which he said was "consistent with final preparation for suicide operations".

He added that a cache of weapons and ammunition had also been found in the raid and destroyed.