BAGHDAD - Iraq hopes to complete its first railway link with neighbouring Iran within 18 months, largely to help facilitate the transport of millions of pilgrims that visit Shi'ite Muslim shrines in Iraq each year, a senior transport adviser said.

The roughly 30-kilometre (18.64 miles) line will run between Iraq's southern city of Basra and the Iranian border-town of Shalamja, linking nations with ties that have deepened since the 2003 U.S. invasion of Iraq, after which pro-Tehran Shi'ite Muslim parties enhanced their influence in Baghdad.

"We should see the trains moving in about 18 months because it's a small distance," Nasser Al-Asadi, transport advisor to the Iraqi prime minister, told Reuters.

He added the government also planned a metro link between Karbala and Najaf, the seat of Iraqi Shi'ite clergy.

Iraq and Iran fought a devastating eight-year war in the 1980s, during which much of the border area was heavily mined.

But since the U.S. toppled former leader Saddam Hussein in 2003, Shi'ite Muslim parties close to Tehran have become key political players in Baghdad and economic and religious ties between both nations have expanded.

Asadi said work was underway to clear the area before ground work could begin on the rail link.

Regularly, the world's largest annual religious gathering of up to 20 million mostly Shi'ite Muslims takes part in the 'Arbaeen' pilgrimage to Iraq's holy city of Karbala to commemorate the slaying of Imam Hussein, grandson of the Prophet Mohammed.

Many pilgrims walk hundreds of kilometres from the Iran-Iraq border to Karbala, or drive there in overcrowded cars and buses, and deadly accidents have been frequent.

Asadi said the rail link would reduce the risk of such accidents and allow Iraq to benefit financially from ticket sales.

The projects are part of major transport-sector development planned by the government, including an overhaul of Baghdad's international airport and a 1,200-kilometre (745.65-mile) rail, road and services project from a major commodities port in the south to its border with Turkey.

(Reporting by Timour Azhari; Editing by Bernadette Baum)