Jakarta – Illegal levies on trucks carrying relief supplies to tsunami-devastated Aceh province is adding to the costs of reconstruction, and Indonesia must crack down on the practice, the World Bank and the agency in charge of rebuilding said Tuesday.

Trucks must pay around $35 in bribes at dozens of makeshift posts manned by police, as well as at two government weigh stations, on both legs of the journey from Medan to Banda Aceh, a study by both institutions found. Medan is a large port city on Sumatra Island, and the main hub for relief supplies to Aceh.

"Bringing down these costs, and ensuring that fees levied are legal and paid into state coffers, must be a priority," the report said. "These extra costs are having an impact on the tsunami reconstruction process."

The study found that instances of extortion on the highway dropped in the aftermath of a peace deal between rebels and government forces in August that saw tens of thousands of troops gradually withdraw.

However, charges levied at weigh stations increased, and trucks must also pay money to military-linked criminal gangs in Medan before setting off to assure smooth and safe passage, it said. The survey was based on observations of 59 truck journeys from early November last year to February 2006.

The Dec. 26, 2004 tsunami that killed or left missing at least 216,000 people in 11 nations generated some $13 billion in aid – one of the most generous global responses ever to a natural disaster.

Relief organizations in hardest hit Indonesia pledged to carefully audit their funds amid concerns that aid dollars could be stolen by corrupt officials or contractors in the country, which is rated as one of the world's most graft-ridden.