ISIS is using Fallujah residents as human shields and preventing civilians from leaving the Iraqi city, the country's High Commission for Human Rights said in a statement Tuesday.

The terror group, which controls large swaths of territory across Iraq and Syria, is apparently readying for an expected offensive by powerful Shiite militias who have vowed to drive the group out of the Anbar Province city 40 miles west of Baghdad, the Washington Post noted.

Eid Amash, a spokesman for Anbar's provincial council, told BasNews ISIS had recently opened fire on local families who had attempted to flee the city at night, a claim also leveled by High Commission for Human Rights member Fadel al-Gharawi.

"(ISIS) has been using civilians as human shields in Fallujah for more than three months, preventing them from leaving the city and confiscating the property of anyone who disobeys," al-Gharawi said. "Insurgents have planted improvised explosive devices in all of the city's mosques and residential buildings and along the roads that lead to Fallujah."

Some 1,000 families, however, managed to flee the city as the Hashd al-Shaabi militia was able to secure a road out of Fallujah late Monday, BasNews reported. The Shiite group is allied with the Iraqi army.

Within the city, the expected assault has led to panic, the Washington Post reported, even though militia leaders have cautioned any attempt to enter Fallujah itself may still be weeks or months away. An estimated 50,000 civilians remain in the city, and mosques have called on residents to donate blood this week to help treat people wounded by possible bombardments.

Qais al-Khazali, the leader of Asaib Ahl al-Haq, another Shiite militia, announced, "The next battle will be in Fallujah," and taunted ISIS militants to hold off Iraqi forces as long as they did the U.S. Marines in the city's notorious battle in 2004.

"Victory is guaranteed," al-Khazali said.