A statement from the premier's office says al-Abadi was the first to pass through the newly-opened Green Zone, or the International Zone as it is officially known.
A senior Green Zone security official tells The Associated Press that much of the restrictions on the Green Zone will still remain in place, particularly on streets leading to high-level government buildings and embassies, including the US embassy.
The official spoke anonymously because he is not authorised to brief the media.