AMIRIYAT FALLUJA, Iraq — More than a thousand Iraqi Sunni fighters stood at attention, dressed in camouflage but holding no weapons, as the tribal leader began exhorting them to fiercely battle the militants of the Islamic State, taking up rhetoric tinged with Arab notions of vengeance.

“It is now time for revenge for our martyrs,” said the sheikh, Falih al-Essawi, who was dressed in a military uniform. He checked off the destruction wrought in their lands by the Islamic State, or, as he called them, “the rats of ISIS”: 25,000 homes leveled, he said, bridges burned, the economy devastated.

He and other speakers made an explicit plea to the Shiite prime minister in Baghdad, Haider al-Abadi: Arm and support our men, and we will take the fight ourselves to the Islamic State.

That event was 11 days ago at a military base here in Amiriyat Falluja, one of the last cities of Anbar Province in government hands. It was billed as the beginning of a government program to arm and train local Sunni tribesmen to battle the Sunni extremists of the Islamic State — a critical gesture to show that Shiite and Sunni Iraqis could unite in the fight, and to put Sunni residents at ease with defenders from their communities.