Fighters from the Islamic State of Iraq and the Levant (ISIL) group have killed 18 Iraqi soldiers in a suicide car attack north of Ramadi, continuing their counterattack after being driven from the city by Iraqi troops last month.

Military sources told Al Jazeera that Tuesday morning's attack took place in the town of Al-Bu Dhiaab, just a few miles north of Anbar province's capital.

Three ISIL suicide bombers attempted to attack members of the 39th brigade of the 10th army division, but two of their vehicles were demolished by anti-tank missiles, the military sources said.

The third bomber, however, managed to make his way to the gate of the army's headquarters and detonate the explosives, killing at least 18 soldiers.

Al Jazeera's Imran Khan, reporting from Baghdad, said: "This is a major blow for the Iraqi Security Forces (ISF). The north of Ramadi was supposed to be secure."

He said that it was too early to say that ISIL's recent attacks against Iraqi forces around Ramadi could be labelled a "resurgence".

"What we do know is that ISIL is able to mount attacks because they are a lot more nimble," our correspondent said.

The Iraqi army declared Ramadi liberated in early January after a major offensive reclaimed government offices in the city centre.

But since then, Iraqi forces have faced continued attacks from ISIL and fierce resistance in areas it holds in Ramadi's suburbs - with dozens of Iraqi soldiers killed in attacks last week.

Elsewhere, in Ramadi's eastern Shujirayah neighbourhood, Iraqi forces were attempting to clear about 300 ISIL fighters believed to be holed up there.

"This is the fourth time Iraqi forces have mounted an offensive to take these eastern neighbourhoods, the last remaining pocket of ISIL fighters," Al Jazeera's Khan said.

He said booby traps set by ISIL have so far slowed the advance.

Al Jazeera