Militants took control of most of the western Iraqi town of Hit in Anbar province early on Thursday, Reuters reported security sources and local officials as saying, Al Arabiya reported.
"Ninety percent of the town of Hit has been overrun by militants," said Adnan al-Fahdawi, a provincial council member.
In an interview with BBC on Wedneday, Iraqi Prime Minister Haider al-Abadi Abadi said "we have contained this [ISIS] threat, but being in a battle and having looked at the threat they posed before, I cannot guarantee 100 percent [that] their existential threat is not there."
He described the threat emanating from ISIS as one that affected the international community, including regional countries such as Iran.
"I am asking for all international efforts," Abadi told the BBC, adding "I want an international umbrella, I don't know what is going to happen in the future."
Meanwhile, Australian air force personnel have completed their first operational missions in Iraq as part of efforts to combat ISIS but Baghdad said it was still considering if Canberra could join air strikes.
Iraq's ambassador to Australia on Thursday gave no timetable for when his government might decide on Australia's request to launch airstrikes against ISIS, the Associated Press reported.
Australia has six F/A-18F Super Hornet jet fighters waiting on standby in the United Arab Emirates for final authorization to begin combat missions with the U.S.-led coalition.
"We are seriously considering the request from Australia," Ambassador Mouayed Saleh told The Associated Press.