Hundreds of extremists were feared to be on the run in Iraq on Monday after al-Qaida's affiliate in the country launched a major assault on the infamous Abu Ghraib prison, offering a fresh boost to the group's resurgent fortunes in Iraq and in Syria.

Iraq's Interior Ministry said in a statement that an unspecified number of prisoners had escaped from Abu Ghraib but none from a second facility that also came under assault. In Washington, U.S. officials closely monitoring the jailbreak said the number of escapees was thought to be 500 to 600, including a significant number of al-Qaida operatives.

Members of the Iraqi parliament who said they had been briefed by security officials asserted that the escapees included some top "emirs," or leaders, of the al-Qaida in Iraq franchise, many of whom had been captured by U.S. troops.