Nine rockets landed around the , home to government buildings and foreign missions, the military said, shortly before amid a protracted political deadlock.
Several members of the security forces were injured in Thursday's attack, the statement added without giving further details.
Similar attacks took place last month as the parliament was holding a vote to confirm its speaker.
A Reuters witness and parliament sources said that they saw at least three rockets landing in the Green Zone.
There was no immediate claim of responsibility.
Rocket attacks on the Green Zone have happened regularly in recent years but they are normally directed at Western targets by Iran-backed militia groups.
Thursday's vote comes amid deep political divisions that have led to a year-long stalemate. Parliament convened shortly after the missile attack.
(Reuters)