IRBIL, Iraq – A recent Islamic State offensive in Iraq's Anbar Province suggests that the extremist organization is changing tactics, relying less on local Sunni Muslim tribes for support and carrying out what one coalition strategist called a "counterinsurgency campaign" intended to undercut any U.S.-led effort to enlist tribes against it.

The outlines of this new strategy became apparent last week when the Islamic State of Iraq and the Levant (ISIL) launched an assault on Ramadi, capital of Anbar Province, without the assistance of local fighters. That assault was preceded by weeks of assassinations aimed at prominent ­members of Anbar tribes.

"This is the first real multipronged assault by the group acting on its own," said Aymenn al-Tamimi, a Middle East-based researcher who studies jihadist groups in Iraq and Syria, referring to the campaign, which began last Friday.

ISIL's success over the summer is due in part to Sunni tribes joining in its campaign against the Shiite Muslim-led government of then-Prime Minister Nouri al-Maliki. Since then, however, two developments have undercut that cooperation: Al-Maliki has been replaced by Haider al-Abadi, who's considered more palatable to Sunnis than Al-Maliki, and ISIL has asserted itself at the expense of local factions in the areas of Iraq it controls.

"Coordination might have been fashionable at the start of the renewed insurgency at the beginning of this year," ­Al-Tamimi said, referring to cooperation between Sunni tribes and ISIL dating to ­January. "But it seems to have dropped off."

As the provincial capital, Ramadi is the key to control of Anbar Province and would be an important steppingstone for any eventual advance on Baghdad. Much of the province is already under ISIL control, including the city of Fallujah, where the U.S. conducted two bloody offensives against jihadist forces during its occupation of Iraq.

Ramadi has been contested for nearly a year between ISIL forces and those loyal to Baghdad. U.S. officials, in an effort to break ISIL's alliance with Sunni tribes, plan to arm Sunni tribesmen with more than $24 million worth of weaponry and supplies, including AK-47 assault rifles, rocket-propelled grenades and mortar rounds, according to a document prepared for Congress. The U.S. also plans to send hundreds of U.S. troops to Anbar to help train Sunni tribesmen.

Some analysts say the U.S. plans, and the recent government capture of Baiji in Salahuddin province, may be behind the ISIL's new strategy of working to undercut possible new enemies.

That's likely to spell an increasingly brutal fight for Anbar. "Things are going through a dangerous phase," said Hikmat Sulayman Ayada, the head of the Anbar provincial council's security ­committee.