Islamic State fighters have closed in on Baghdad and are now reported to be less than 10 miles away from the Iraqi capital.
Some units of the extremist group, previously known as Isis, have reached the suburb of Abu Ghraib, home to the infamous prison, which lies only eight miles from Baghdad international airport, according to CBS news.
Although the Iraqi army is said to be still in control of the district, the development sheds a worrying light on the government's ability to stop IS advance.
Despite US-led airstrikes against them, the jihadist group has made substantial gains in the western Anbar province in recent weeks.
IS captured Fallujah in January and has since expanded its hold in the province. In September the group renewed its offensive and is now in control of more 80% of the province, Iraqi officials said.
"Isis has conducted a sophisticated campaign in Anbar Province over the past four weeks in order to capture additional cities in the Euphrates River Valley," the Washington-based Institute for the Study of War (ISW) said.
"It has consolidated its supply route from Syria into central Iraq, gained freedom of movement in both countries, and received reinforcements for the Anbar offensive probably from its safe havens in the Albu Kamal area in Syria; Mosul; and Iraq's Lake Thar Thar region.
"Ultimately, Isis aims to surround Baghdad from its belts," ISW said.
During its advance, in September IS seized the Iraqi military base of Camp Saqlawiyah 45 miles (70km) west of Baghdad amid claims that the government failed to provide adequate support to its troops stationed there.
Earlier this month, IS captured Hit, Anbar's fifth largest city, and is now threatening the nearby al-Asad airbase. The strategic town of Ramadi, which has seen intense fighting in recent days, is reportedly about to fall.
"If Ramadi falls, all of Anbar falls," Ahmed Abu Risha, a prominent tribal sheikh at the head of a pro-government fighter unit in the area, told The Washington Post. "Ramadi is the head. If you cut the head, the rest of the body will die, too."
Security experts said that once in full control of the province, Islamist militants might be able to hit targets in the capital.
"The government would lose the Haditha Dam, and the security forces would have to retreat," Iraqi security expert, Saeed al-Jayashi told the US paper. "There would be a blood bath."