Iraqi forces remain on the defensive against the Islamic State in western Iraq, unable to protect the tribesmen who U.S. and Iraqi officials are betting will throw their weight behind the fight against the militant group, U.S. military leaders said Thursday.

“The Iraqi security forces in al-Anbar province are in defensive positions and would be unlikely to be able to respond to a request for assistance for the Albu Nimr tribe,” Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told reporters at the Pentagon.

This week, Islamic State fighters publicly executed dozens of Sunni tribesmen, most of them from the Albu Nimr tribe, in the western Iraqi city of Hit. It was the militant group’s latest bloody signal to Sunni Muslims who may be considering taking up arms against them.

Some reports put the number of tribesmen slain by the Islamic State in western Anbar province at more than 200.

The killings raise additional questions about efforts by Iraq’s Shiite-led government, backed by the United States, to encourage a new tribal uprising that officials from both countries believe is critical to turning the tide against the Islamic State.

Dempsey said he did not know of any requests from the Albu Nimr tribe for help from the Iraqi military or from the United States, which is bombing Islamic State targets across Iraq.

On Monday, U.S. cargo planes dropped more than 7,000 meals to Iraqi forces around Ayn al-
Asad military base, which were then delivered to Albu Nimr tribesmen who had fled Hit. But the Iraqi soldiers appear unable to venture out from the base to come to the rescue of tribesmen in areas controlled by the Islamic State.

The Iraqi forces’ inability to help nearby civilians is another indication of the challenges the United States and its allies face in reestablishing security in Iraq.

Much of Iraq’s army collapsed in June as Islamic State fighters advanced across northern Iraq. Now, with a new government in Baghdad, U.S. officials are focusing on helping Iraq restructure and reform its military, a task made all the harder by ongoing militant assaults.

Dempsey said the Iraqi army was hindered in part by the isolated location of many of its major bases, which may make it more difficult to resupply and reinforce soldiers and make them more vulnerable to militant attacks.

“The systematic execution of Sunni tribesmen . . . and the brutality, that’s what we’re dealing with,” said Defense Secretary Chuck Hagel, who spoke alongside Dempsey. “This is why bringing a coalition together, this is why engaging the Sunni tribesmen in a reformed Iraqi security force where they have some confidence . . . all of that has to come together.”

Since he took office in August, Iraqi Prime Minister Haider al-Abadi has been courting support from Sunni tribesmen in western and northern Iraq. American officials hope Abadi can re-create the Sunni tribal movement that helped defeat al-Qaeda in Iraq in Anbar in 2006-2007.

Dempsey said he would like to see U.S. soldiers, who have returned to Iraq to advise local forces, expand their mission in Anbar.

“The precondition for that is that the government of Iraq is willing to arm the tribes,” he said.