At least 13 people were killed by a car bomb in Baghdad on Saturday, police said, in one of the deadliest attacks in the Iraqi capital this year.

A police colonel told AFP "at least 13 people were killed and 39 wounded in a car bomb facing a popular restaurant in the Karrada area".

Karrada is packed with shops and restaurants and would have been busy on Saturday night, which marks the end of the weekend in Iraq.

No one has so far claimed responsibility for the attack, which comes after a series of similar bombings in the capital.

Eleven people were killed and more than 40 wounded in a wave of car bomb attacks on Thursday and another nine were killed in two car bombings in Baghdad on Monday.

The Islamic State jihadist group claimed it had carried out those attacks on Shiite districts of Baghdad to avenge attacks on displaced persons from a Sunni province.

Since the start of April, 114,000 residents have fled fighting between government forces and IS in the Ramadi area of the western province of Anbar, which is largely controlled by the Sunni extremist group, according to UN figures.

Police say several of the displaced have been kidnapped and killed in Baghdad, including four victims found on April 25 with gunshot wounds to the head.

Despite the recent attacks, they have decreased sharply in number compared to the same period last year.

Bombings and shootings in Baghdad were once a daily occurrence, but have declined since Islamic State launched a major offensive last June, seizing control of vast areas north and west of the city.

That has tied them down in fighting outside Baghdad that distracts from their ability to carry out attacks inside the capital.

A curfew in operation for years in the Iraqi capital was lifted in February.

The Iraqi army has taken back some territory from the Islamists and in April, troops seized back control of the city of Tikrit, its biggest victory of the 11-month conflict.

But many other areas remain under IS control.