Iraqi Prime Minister Haider al-Abadi on Sunday announced that Baghdad's "Green Zone" was open to the public for the first time in 12 years, albeit with many remaining restrictions.

The roughly 10-square-kilometre (four square miles) heavily fortified area in the heart of Baghdad is home to the country's top political institutions and embassies.

"The prime minister opened the Green Zone to public passage and people in their vehicles came in droves," a statement from Abadi's office said.

"The opening of the Green Zone is one of the measures we promised the people and we are opening it now," Abadi was quoted as saying in the statement.

The measure offers limited access to the vast area, with most streets still requiring a special badge, but it is likely to be popular nonetheless and ease traffic congestion.

The International Zone of Baghdad was already the seat of government power under former president Saddam Hussein and became known as the Green Zone after the 2003 US-led invasion.

The area, nestled in a bend of the Tigris River, was then sealed off to the public and became the headquarters of Iraq's new masters.

The Green Zone is home to the offices of the president, prime minister, to parliament, the country's top courts and the US embassy, which is the world's largest.

The area's foreign residents still sometimes refer to what lies beyond the miles of concrete walls and concertina wire as the "Red Zone".

The term Green Zone has for many Iraqis become synonymous with the disconnect between the country's rulers and the harsh realities of ordinary citizens.

Iraqis have frequently complained that their leaders lived a sheltered existence in the safety of the Green Zone, its luxury villas and broad avenues, while they suffered from daily violence and abysmal services.

In his statement, Abadi presented the partial reopening of the area as part of the reform drive he launched to address mounting popular discontent over corruption and poor services.

"We are going forward with our reforms and we will not relent," he said.

The Green Zone has been repeatedly targeted over the years, especially at the height of the 2006-2008 civil conflict.