Protesters storm fortified Green Zone in Baghdad

Anti-government protesters stormed Baghdad's heavily fortified Green Zone on Friday, heightening concerns about political stability at a critical time in Iraq, Reuters reported.

Iraqi security forces fired weapons in the air and used tear gas as hundreds of protesters breached the walls and rushed toward the prime minister's office and the parliament building, according to the Associated Press.  Some protesters had been wounded. The violence caused Iraqi Prime Minister Haider al-Abadi to impose a curfew in Baghdad, the AP reported.

It was the second such protest in less than a month and comes amid growing violence in the capital. A spike in bombings attributed to the Islamic State has killed scores in recent weeks.

The Green Zone, once the U.S. military and administrative headquarters, houses Iraqi government offices and Parliament.

The earlier protests at the fortified compound had been instigated largely by followers of Muqtada al-Sadr, a Shiite cleric who wields political influence in the country. During the protests in April, security forces allowed the protesters to scale the walls into the Green Zone. The government security forces appear to be taking a more active role this time.

The political instability in Iraq threatens to undermine the U.S.-backed efforts to drive Islamic State militants, also known as ISIS or ISIL, from the country. The Islamic State has lost 45% of the territory it once held in Iraq and 20% of areas it controlled in Syria, according to recent estimates by a U.S.-led coalition combating the extremist group.