The coordinated attacks on Taji prison, north of Baghdad, and Abu Ghraib, west of the capital, were launched last night and triggered fighting that raged for around 10 hours, officials said.
Abu Ghraib prison, already infamous as a centre for the torture of opponents of now-executed dictator Saddam Hussein's regime, gained further notoriety in 2004 when graphic pictures emerged showing prisoners being humiliated and abused by their US guards.
A frenzy of comments posted on social media, including some Twitter accounts apparently operated by jihadists, claimed that thousands of prisoners had escaped.
"About 500 prisoners escaped from Abu Ghraib prison," Hakem al-Zamili, a member of the parliamentary security and defence committee, told AFP.
More From This Section
He said the escaped prisoners were "terrorists" but that, to his knowledge, no inmates managed to break out from Taji.
However, MP Shwan Taha, also a security and defence committee member, said in an online statement that between 500 and 1,000 inmates escaped from the two prisons.
Officials said at least 20 members of the security forces were killed and 40 wounded in the attacks. And the justice ministry's spokesman said 21 inmates were killed and 25 wounded in rioting at the prisons.
The attacks were launched at around 9:30 pm (local time) yesterday when the militants fired mortar rounds at the prisons.
Car bombs were detonated near the entrances to the prisons, while three suicide bombers attacked the Taji prison, a police colonel said. Five roadside bombs also exploded near the prison in Taji.
Fighting continued throughout the night as the military deployed aircraft and sent in reinforcements around the two facilities.
The situation was eventually brought under control this morning, according to the colonel.