Baghdad, Iraq (CNN) -- Militant fighters tightened their grip Sunday on western Iraq as security forces withdrew from a handful of towns in Anbar province, moving closer to Baghdad.
The news that Iraqi forces withdrew from at least three towns in the province raised questions about whether Prime Minister Nuri al-Maliki's government is giving up on the region.
It also comes the same day that Iran's religious leader condemned any U.S. involvement in Iraq, saying al-Maliki's government can handle its own problems.
"The United States is trying to portray this as a sectarian war. But what is happening in Iraq is not a war between Shiite and Sunnis," Ayatollah Ali Khamenei said in a statement carried by the state-run IRNA news agency.
He blamed the attacks in Iraq on the remnants of Saddam Hussein's regime and extremists.
But U.S. Secretary of State John Kerry, speaking from Cairo, said no one should mistake what is happening and why.
"This is about (ISIS) designs on the state of Iraq," he said. "... The United States is prepared to help Iraq stand up against that."
As part of that effort, Kerry called on al-Maliki's Shiite-dominated government to rise above "sectarian motivations" to become more inclusive, more representative of its population.
Closer and closer to Baghdad
As international pressure mounts on al-Maliki, ISIS fighters continued their advance from the west and north on Baghdad.
Iraqi security officials told CNN that Tal Afar airbase in northern Iraq was taken by militants believed to be ISIS on Sunday afternoon.
Militants took over the town of Tal Afar last week but by Sunday, they also controlled the air base completely, officials said. Thousands of Shiite Turkmen families fled the town last week when ISIS attacked the town.
The western Anbar town of Rutba, 113 kilometers (about 70 miles) from the borders of Jordan and Saudi Arabia, was in the hands ISIS fighters, two security sources in Baghdad and one in Anbar told CNN on Sunday.
With the capture Saturday of Qaim on the border with Syria, where ISIS enjoys a stronghold, and a number of other towns in Anbar province, the fighters now have a direct line to the western outskirts of Baghdad.
At least 70% of the province is under the control of ISIS, two security officials in the region told CNN.
Iraqi forces withdrew from Haditha, about 270 kilometers (about 168 miles) northwest of Baghdad, during the overnight hours, two security officials in Anbar, speaking on condition of anonymity, told CNN.
Sunni tribes considered friendly to the Iraqi army took over security for the town, but officials believe it will fall to ISIS, said the officials, who are not authorized to speak to the media.
Haditha is home to the largest hydroelectric plant in Anbar, which is vital to the water supply of the province.
Iraq's military spokesman, Maj. Gen. Qassim Atta, told reporters there was a "strategic withdrawal" in some areas but did not detail the specific locations.
He said the withdrawals were part of a campaign to "open all these fronts so we can strengthen our positions."
Even so, there is a question of whether Iraqi forces can retake the regions under the control of well-armed ISIS fighters.
The fighters launched an attack during the overnight hours against one of the two remaining military bases in Anbar, two security officials in the province told CNN.
The fighters attacked Khalidiya military base, near Ramadi, but were unable to take it and withdrew early Sunday, the officials said.
Al-Asad, a large Iraqi air force base, and the nearby town of Hit are still under the control of the central government. The expectation, the officials say, is that both will be attacked next.
Despite the government effort to protect the Iraqi capital, minor clashes were reported between Sunni insurgents, possibly ISIS fighters, and Iraqi security forces in the Sunni town of Abu Ghraib very near Baghdad's western border, according to security officials.
Violence elsewhere in Iraq
Sporadic violence was reported across Iraq, including in the Shiite-dominated city of Hillah, about 95 kilometers (60 miles) south of Baghdad, where a recruiting station was shelled.
At least four people were killed and 34 were wounded in the attack on the recruiting station, where hundreds of predominantly Shiite men were answer a call to arms to protect Iraq.
In the northern city of Mosul, site of one of the first major victories for ISIS militants, witnesses told CNN on Sunday that the group used vehicle-mounted loudspeakers to announce that it had decided to form Islamic Sharia courts in the city.
The group also reportedly removed statues of the Christian Virgin Mary, Arab poet Abu Tammam and singer Mulla Othman, witnesses said.
The Iraqi government was waiting for the initial group of U.S. military advisers to arrive in Iraq soon, a senior defense official said.
This first detail is expected to be very small, the official said. The total number of U.S. military advisers who will eventually deploy will be about 300.
In addition, some U.S. military personnel already at the U.S. Embassy in Baghdad will be reassigned and become advisers, Pentagon spokesman Rear Adm. John Kirby said.
CNN's Nic Robertson and Nima Elbagir contributed from Baghdad, and Arwa Damon from Irbil, Iraq. Mohammed Tawfeeq contributed from Atlanta. Michael Martinez wrote from Los Angeles.