A double bombing has rocked an Iraqi city north of Baghdad, leaving at least seven people killed, officials said.

The attack on Saturday morning took place when a roadside bomb exploded in a commercial street in the northern city of Tikrit.

Minutes later, a car bomb struck policemen who had arrived to inspect the first blast.

The officials said five policemen and two civilians were killed and 18 people were wounded in the bombings. A medical official confirmed the casualty figures.

Tikrit is 130 kilometres north of Baghdad.

The latest blast comes a day after a series deadly attacks across Iraq killed and injured dozens of people.

The deadliest attack on Friday occured in the village of Injanah, 55km north of Baquba, when an explosive-laden tanker was driven into the federal police headquarters, killing at least 15 people.

In Ramadi on Friday, 12 people were killed when a suicide bomber blew himself up inside a mosque where a funeral was being held for an officer who died in a roadside bombing earlier this week, medical and security sources.

Violence has spiked in Iraq since last April, a surge unseen since 2008.

The relentless attacks have become the government's most serious challenge.