The chief internal watchdog at the state department has been accused by former and current officials of systematically interfering with investigations to protect the White House from political embarrassment.

Henry Waxman, the chairman of the House oversight committee, said the officials had contacted his office to complain that Howard Krongard, the state department’s inspector-general, “repeatedly halted or impeded” investigations undertaken by his office, including probes into wasteful spending and procurement fraud in Iraq and Afghanistan.