The Bush administration is blocking an inquiry into the delay-plagued construction of the $736m US embassy in Baghdad, a senior Democrat in Congress said today.

Henry Waxman, who is chairman of the oversight committee in the House of Representatives, asked US secretary of state Condoleezza Rice today to explain why her department certified the embassy as "substantially completed" in December despite inspections that reveal continued deficiencies in the facility's water, fire alarm and kitchen systems.

The Baghdad embassy, which stands to become the largest US diplomatic facility in the world, had an original opening date of mid-2007. But the project stalled amid ballooning cost estimates as well as charges of corruption and shoddy work by the private contracting company overseeing the project.

In addition, two US state department employees who worked on the embassy project are now under criminal investigation. Waxman urged Rice to release subpoenaed documents related to the Baghdad embassy project next week or risk being forced to do so.

"It appears that the state department is concealing from Congress basic information about the status of the embassy project and the activities of the individuals and contractors involved," Waxman wrote to Rice. "This continued intransigence is inappropriate."

The private construction company, First Kuwaiti General Trading & Contracting, declined repeatedly to provide safety inspectors with reports on fire protection systems at the embassy, according to reports released by Waxman. First Kuwaiti, based in Kuwait, remains the target of a separate US criminal probe into allegations of labour trafficking.

The state department has not yet received Waxman's letter but plans to address the Democrat's concerns by his March 7 deadline, spokesman Tom Casey told reporters today.

Casey defended the delay in construction of the embassy, asserting that the building would not be occupied until its fitness for use could be certified.

"[W]e certainly have no intention of taking occupancy or establishing occupancy in a facility that doesn't fully meet all our standards," Casey said. He reminded reporters that First Kuwaiti is required under its contract to bear the cost of any needed additional work.

The new director of building operations at the state department has ordered a review of the embassy project and may revoke the building's "substantially completed" certification, McClatchy news service reported this week.