Iraqi government forces battling an al-Qaida offensive have launched an air strike on the city of Ramadi, killing 25 Islamist militants, according to local officials.

Local government officials in western Anbar province have met tribal leaders to urge them to help repel al-Qaida-linked militants who have taken over parts of Ramadi and Falluja, strategic Iraqi cities on the Euphrates river.

Al-Qaida's Islamic State of Iraq and the Levant (ISIL) has been steadily tightening its grip in the vast Sunni-dominated Anbar province in recent months in a bid to create a Sunni Muslim state straddling the frontier with Syria.

But last week's capture of positions in Ramadi and large parts of Falluja was the first time in years that Sunni insurgents had taken ground in the province's major cities and held their positions for days.

Local officials and tribal leaders in Ramadi said 25 suspected militants were killed in the air force strike, which targeted eastern areas of the city early on Sunday.

"As a local government we are doing our best to avoid sending the army to Falluja … now we are negotiating outside the city with the tribes to decide how to enter the city without allowing the army to be involved," said Falih Eisa, a member of Anbar provincial council.

Tension has been running high across Anbar – which borders Syria and was the heart of Iraq's Sunni insurgency after the 2003 US-led invasion – since Iraqi police broke up a Sunni protest last week, resulting in deadly clashes.

In Falluja, ISIL's task has been made easier by disgruntled tribesmen who have joined its fight against the government.

Further west, across the porous border with Syria, al-Qaida fighters have captured swaths of land in the north and are battling with other Islamist brigades as well as the Syrian army.

In Ramadi, where tribesmen and the army have been working together to counter the al-Qaida insurgents, ISIL snipers positioned themselves on rooftops and fought small battles in the city.

ISIL fighters held on to their positions in the outskirts of Falluja and have used police and government vehicles inside the city for patrols, some flying a black flag associated with al-Qaida from the vehicles.

The US secretary of state, John Kerry, said on Sunday that Iraq's government and tribes would be successful in their fight against al-Qaida, and said Washington was not considering sending troops back to Iraq, two years after their withdrawal.