The United States wasted nearly $500,000 on an Afghan police training center that began to fall apart only months after it was built due to shoddy contractor work, according to a watchdog report released Thursday.

The center's adobe-style brick buildings were supposed to replicate an Afghan village to allow the country's special police to practice search operations but the roof and walls began "melting" away in the rain four months after it was completed, said the report by John Sopko, Washington's special inspector general for Afghanistan reconstruction (SIGAR).

"Therefore, although this project may have been well intentioned, the fact that the Afghans had to demolish and rebuild the DFR (dry fire range) is not only an embarrassment, but, more significantly, a waste of US taxpayers' money," Sopko's office said.

The report found that US officials failed to properly supervise or hold accountable the Afghan firm selected to build the center, Qesmatullah Nasrat Construction Company, which used substandard bricks and failed to follow contract requirements.

The inspector general's report is the latest in a long series that have found massive waste and botched projects worth billions of dollars across Afghanistan.

For the police training center in eastern Wardak province, American officials at Forward Operating Base Shank awarded the $456,669 contract to the firm in May 2012. And the company was paid in full once the buildings were completed in October of the same year.

The center "was not constructed according to contract requirements, and our analysis showed that, as a result, water penetration caused its walls to begin disintegrating within 4 months of when the US government accepted the project . . .," the SIGAR report said.

- Bricks made of sand -

The firm installed roofs without gravel and asphalt, failed to ensure a slope to the roof to allow water to drain to collection points, used smaller bricks than required and of insufficient strength, it said.

The bricks "were made mostly of sand with little clay content and that the lack of adequate clay material caused the bricks to fail when water penetration occurred," it said.

The report included photos that showed the buildings intact just after construction was completed, then with massive leaks and disintegrating walls in the following months.

US officials eventually concluded the building was completely unsafe and would have to be rebuilt entirely. The contracting company initially planned repairs but was not ready to rebuild the entire facility, it said.

The Afghan government has since demolished the buildings and is now rebuilding the training center.

The report urged US Central Command to try to recoup funds where possible, determine why the compound was not built according to contract requirements and what disciplinary action should be taken against contracting officials.

Central Command accepted the report's recommendations and said it plans to take corrective action.

Sopko has warned that it will be difficult to track reconstruction projects as international troops withdraw.

Most of a NATO-led force has pulled out of Afghanistan and a small force of about 12,000, made up mostly of American troops, remains deployed.