The ISIS thrust toward Khalidiya came as top Iraqi government officials backed the Iraqi Prime Minister's decision to move more Shiite militia members into the largely Sunni Anbar province in a multipronged effort to defeat ISIS there.
Using mortars and rocket propelled grenades overnight into Tuesday, ISIS attackers took aim at Iraqi security forces and Sunni tribesmen defending Khalidiya, a city 25 kilometers (16 miles) to the east of Ramadi, a security official and two witnesses said.
The defenders pushed the ISIS fighters back, but sporadic attacks continued Tuesday, the three sources said. Details about casualties weren't immediately available.
ISIS already controls an Anbar city even closer to Baghdad -- Falluja. Were ISIS to capture Khalidiya, it would be closer to establishing an ISIS-controlled corridor along the Euphrates River between Ramadi and Falluja.
Tribal and local forces have set up defensive lines west of the cities of Khalidiya and Husaybah, said Ibrahim Hassan Khalaf al-Fahdawi, head of the Security Council in Khalidiya, and Mahmaoud al-Fahdawi, a leader in the Albu Fahad Sunni tribe. They were joined by a brigade from the Iraqi Federal Police and another from the government's quick reaction forces, the officials said.
Iraqi Cabinet endorses Shiite forces in Anbar
On Tuesday, the Iraqi Cabinet supported Prime Minister Haider al-Abadi's call to put more Shiite militia members into Anbar to push back ISIS.
That plan will further swell the ranks of anti-ISIS ground forces but also could threaten to inflame sectarian tensions.
The decision to mobilize the Hashd Al-Shaabi paramilitary force -- also known as the Popular Mobilization Units -- follows a request for help from Anbar provincial officials, tribal leaders and religious clerics. The Shiite forces helped the Iraqi army retake Tikrit
from ISIS in March.
Al-Abadi met Monday with the group's leadership to discuss plans to retake Ramadi, state-run Iraqiya TV reported.
But the group's involvement prompted fears it could inflame sectarian tensions, and their ties to Iran complicated the use of airstrikes by the U.S. coalition. Iran backs the militia.
Concerns about role of Shiite forces
Muhannad Haimour, a spokesman for Anbar's governor, said the Popular Mobilization Units were no longer Shiite militias but an official body governed by law.
"The governor made the position very clear that any Iraqi who wishes to defend Iraq
is welcome to do so, provided that they are fighting under the Iraqi banner and under the command and control of the Iraqi official security forces," he told CNN this week.
But Robert Baer, a CNN intelligence and security analyst, said involving the Popular Mobilization Units could create "a different bloodbath on its own."
"It would be Sunni against Shia," he said. "Who knows what that would provoke?"
Government says it's committed to arming Sunni tribes
Also Tuesday, the Cabinet said it remained committed to arming Sunni tribesmen opposing ISIS -- a sore subject for the tribes themselves.
In November, the speaker of the Iraqi Parliament told tribal leaders that the government was going to begin arming Sunni tribes in Anbar. But as the months went on, officials in Ramadi repeatedly called for more support and weapons
from the Shiite-dominated government in Baghdad.
Despite their warnings, one of the cities for which U.S. forces fought bitterly in 2005 and 2006 eventually fell to ISIS.
On Friday, the United States announced that it was "expediting" weapon shipments
Fears of 'bloodbath' under ISIS
Now that Ramadi is in the hands of terrorists, officials are "extremely concerned about massacres that we think will be committed by ISIS," said Haimour, the Anbar governor's spokesman.
ISIS has a grim track record of ruthlessly slaughtering opponents it captures.
"Anybody who supported the government will probably be executed within the next 24 hours," Baer said. "Their families will be driven out. It will be a bloodbath over the next couple of days. All the soldiers who were captured will be executed."
Residents have been pouring out of Ramadi toward safer parts of Anbar and Baghdad in recent days.
"We are witnessing a humanitarian crisis," said Haimour, estimating that as many as 8,000 people had left the city Sunday.
Officials estimate that more than 500 people have been killed in the most recent clashes in Ramadi, he said, noting that some pockets of resistance against ISIS remain inside the city.