Baghdad, Reuters—Six suicide bombers burst into an Iraqi ministry building, took hostages and killed at least 18 people including themselves on Thursday before security forces regained control, a senior official said.

The brazen attack on the building belonging to the Ministry of Transportation in northeast Baghdad coincides with a month-long standoff between the Iraqi army and anti-government fighters in the western province of Anbar.

A senior security source said the six militants took a number of hostages and killed four of them inside the building, which was used to receive visiting delegations. It was not immediately known where the other eight victims died.

No group claimed responsibility for the attack, but state buildings are a target for Sunni Islamist insurgents who have been regaining momentum in a campaign to destabilize the Shi’ite Muslim-led government.

More than 1,000 people have been killed in violence across Iraq since the start of the year, when militants seized control of two cities in the Sunni-dominated province of Anbar, bordering Syria.

It is the first time Sunni militants have exercised such open control in Iraqi cities since the height of the insurgency that followed the 2003 US-led invasion that overthrew dictator Saddam Hussein.

Shi’ite Prime Minister Nouri Al-Maliki has asked for international support and arms to help combat Al Qaeda, which has been invigorated by the civil war in neighboring Syria, where it is also active.

Anti-government fighters, including the Al Qaeda-affiliated Islamic State of Iraq and Syria (ISIS), are currently in control of the city of Fallujah, which is being surrounded by the Iraqi army.

The UN refugee agency said the standoff in Fallujah has driven more than 140,000 people from their homes, describing it as the largest displacement in Iraq since the sectarian slaughter that climaxed in 2006-07.