A suicide car bomber attacked Tuesday an Iraqi army recruiting center in northern Baghdad, killing seven people and wounding over 20 others, police said.

"Four National Guard men and three would-be recruits were killed and more than 20 others were wounded," a National Guard officer told Xinhua on condition of anonymity.

In the nearby Nu'man Hospital, a medical source said at least four people died and 23 were injured. "We have received four bodies including those of three soldiers," he said.

The explosion went off at a gate of a vast Iraqi military base in northern Baghdad neighborhood of Adhamiyah, which was one of former president Saddam Hussein's palaces.

A queue of Iraqis who want to join the army were waiting outside the base when the blast occurred, said a young man who was wounded in the left hand and left leg.

"I have come from Najaf to join the army as I have no other way to raise my family," said the man, who refused to be identified.

Iraqi police and US troops immediately cordoned off the area after the blast which broke the relative calm in the past two days in the capital city.

Insurgents have repeatedly targeted US-trained fledgling Iraqi security forces.