Iraq sandstorm Isis
Iraq's Shi'ite paramilitaries involved in the fightback against IS Reuters

Islamic State (Isis) has killed at least 35 Iraqi policemen and Shiite militiamen in a suicide attack on a police base just north of IS-held Ramadi.

The attack on the security service headquarters in Anbar province's Tharthar area is another sign of the slowing counter-attack by Iraqi government forces, working to retake Ramadi after it was overrun by IS in May.

Three Islamic State suicide bombers driving explosive-laden Humvees mounted the attack and the initial blast was followed by a large secondary explosion in an ammunition depot, Iraqi officials told AP, with hospital officials confirming the casualties.

Just days after IS captured Ramadi a counter-attack on the militant group was announced on Iraqi television followed by reports that Baghdad forces were moving to cut IS supply lines to the city.

However, since the beginning of the fightback, government forces have faced a number of setbacks.

Victories in several towns in Iraq's southern Salahuddin province were marred by a series of IS suicide attacks which left at least 17 members of the security services dead with some reports of as many as 55 killed.

On 29 May at least 10 people were killed when car bombs exploded at two luxury hotels in Baghdad.

This most recent attack resembled the massive, coordinated assault launched on Ramadi last month that allowed IS militants to capture the city, marking their biggest gain since a US-led coalition began launching air strikes against the extremist group in August 2014, AP reported.

The loss of Ramadi prompted Iraqi Prime Minister Haider al-Abadi to order Shiite militiamen into the vast Sunni province, which was an insurgent hotbed during the eight-year US intervention.

The Shiite militiamen have played a key role in pushing the Sunni IS group back elsewhere in Iraq, but have also been accused by rights groups of carrying out revenge attacks against Sunnis which make up the majority of the population in Anbar province.

The fall of Ramadi provoked stern criticism of the Iraqi security services by the US.

Speaking in a televised interview with the BBC, the former commander of international troops in Iraq and Afghanistan and ex-director of the CIA General Petraeus has said the capture of Ramadi was: "A strategic loss in the sense that the narrative of IS being on the defensive - of losing - was shown to be somewhat hollow."

However, the retired army chief added that he believed Ramadi could be retaken in a few weeks, or less.