Martin Kobler urged Iraq's political leaders to "engage immediately to pull the country out of this mayhem".

There has been a recent upsurge in violence across Iraq amid rising sectarian and political tension.

Several car bombs targeted different areas of the capital, Baghdad, and the northern city of Mosul on Thursday.

Five bombs killed 21 people in Baghdad and wounded dozens, officials said.

In Mosul, three policemen were killed in an early morning suicide attack.

Earlier in May, Iraqi Prime Minister Nuri al-Maliki warned of attempts to return Iraq to "sectarian civil war."

He called on everyone worried about Iraq's future "to take the initiative, and not be silent about those who want to take the country back to sectarian civil war."

The current violence in the county, he said, “is an intrigue plotted for Iraq, so we call on the politicians to confront this plot by consolidating brotherhood among them and avoid harming their country.”

The dramatic escalation in attacks in recent weeks has raised fears of a return to the levels of sectarian violence seen in 2006 and 2007, in which thousands died.

This week alone, more than 60 people were killed in attacks targeting several areas of Baghdad on Monday. A further 25 deaths were reported in bombings in the city on Wednesday.

The UN has said more than 700 people were killed in April - the highest monthly toll in almost five years. That would take the toll from the last two months well over 1,000 victims.