BAGHDAD, IRAQ - Baghdad municipality has invited international bids to update plans for a 39-kilometre (24-mile) metro aimed at relieving traffic in Iraq's war-battered capital, the city said on Tuesday.

The capital has been choked with cars since sanctions were lifted and customs rates slashed following the US-led invasion of 2003, causing a spike in vehicle ownership that has overwhelmed Iraq's decaying infrastructure.

The situation has been made worse over the past year as security forces have erected miles of walls and hundreds of checkpoints in a bid to halt the sectarian violence which convulsed the city in the years after the invasion.

One metro line would run 18 kilometres from the far side of the eastern Shiite slum of Sadr City to the centre of the city and then up north to the mostly Sunni Adhamiyah neighbourhood, covering 20 stations.

The second line, extending 21 kilometres, would start in the south and pass through the central commercial district of Karrada before crossing the Tigris river and running out to the mostly Sunni neighbourhoods in west Baghdad.

"The municipality has diagrams and designs for the project, but they are old, the information about the metro is old, so we want to update the details with international companies," said Hakim Abdelzahra, a spokesman for the city.

"Parliament has set aside three billion dollars as an estimated cost, but we are waiting for the bids from the companies, which will determine the final cost," the municipality official told AFP.

The plans for the metro date back to the late 1970s and had it been built then it would have been the first urban railway in the Arab world. Instead, the plans were shelved at the start of the devastating 1980-1988 war with Iran.

The finance ministry, meanwhile, plans to raise taxes on cars in 2009 from the flat rate of five percent applied by US authorities after the invasion to 30% in line with the World Trade Organisation.

Baghdad is one of the fastest-growing cities in the world, with a population in 2008 of six million and a growth rate of 4.2%, putting it on track to have more than 10 million residents by 2030, according to the municipality.