The capture of Ramadi is the biggest defeat for the Baghdad government since last summer.
In response, Shia paramilitaries are said to be preparing to deploy en masse to Iraq’s western province of Anbar on Monday the provincial capital was overrun.
A spokesman for the Shia paramilitaries, known as Hashid Shaabi, told Reuters they had received instructions to mobilise, but the timing and scale of the deployment could not be revealed for security reasons.
“Now that the Hashid has received the order to march forth, they will definitely take part,” said Ali al-Sarai, a member of the Hashid Shaabi’s media wing. “They were waiting for this order and now they have it.”
US Secretary of State John Kerry told a news conference in Seoul, South Korea, that Ramadi had been a target of opportunity for the Islamic militants.
“I am convinced that as the forces are redeployed and as the days flow in the weeks ahead, that’s going to change as, overall, (they) have been driven back… I am absolutely confident in the days ahead that will be reversed.”
On Saturday US officials said special forces had carried out a raid inside Syria that killed a man identified as a senior islamic State leader, Abu Sayyaf.
Mr Kerry said the strike had eliminated a “major leader” and resulted in “a significant intelligence gain”.