A spate of attacks across Iraq killed seven people on Thursday, including three who died when a suicide car bomber struck as recruits were leaving a military base, officials said.

The attacks come amid Iraq's worst bloodshed since 2008, with more than 4,000 people killed already this year.

At least one soldier was among three people killed by the car bombing, in the parking lot of a military base in the northern city of Kirkuk, the medical and security officials said.

Another soldier died and two were hurt when a roadside bomb blasted their convoy near the oil town of Baiji, north of Baghdad, while an army captain was killed at a military post in the northern city of Mosul.

Also in Mosul, two civilians were killed in separate attacks on their homes during the night, officials said.

Late on Wednesday, a suicide bomber struck as worshippers streamed out of a Shiite mosque in Baghdad, killing 30 people and wounding 55.

A second suspected suicide bomber spotted at the mosque in the north Baghdad neighbourhood of Waziriyah was shot dead by locals, who then set his body on fire, witnesses said.

The surge in bloodshed has sparked concerns that Iraq is slipping back into the all-out sectarian war that plagued the country in 2006 and 2007, leaving tens of thousands dead.

Experts say militant groups are exploiting political infighting in Iraq and regional sectarian tensions fuelled by Syria's civil war to recruit and to carry out attacks.