A suicide car bomb hit a military checkpoint outside an Iraqi-US base in Tikrit on Sunday, killing three Iraqis and wounding at least 18 others, police said.

"The attack took place at about 10:00 a.m. (0600 GMT), when a suicide car bomber drove an explosive-laden vehicle into a checkpoint of a US-Iraqi military base," a source from Tikrit police told Xinhua on condition of anonymity.

"An Iraqi soldier and two civilians were killed in the attack, and more that 18 people were wounded, including several soldiers," the source said.

The attack occurred outside the base that houses a joint US- Iraqi coordination center in Tikrit, some 170 km north of Baghdad, the source said.

US and Iraqi forces sealed off the area as ambulances evacuated the victims to Tikrit Hospital for treatment, the source said.

Insurgents have stepped up attacks on Iraq's army and security forces since a Shiite-dominated government was announced in late April, killing more than 900 people.

Source: Xinhua