The Transportation Security Administration is defending its operations at Newark Liberty Airport in New Jersey following a report last week that an undercover inspector sneaked a simulated explosive past security.

The TSA said Wednesday on its blog that it's conducting tests that some officers are prone to fail - to improve performance and stay a step ahead of adversaries.

The New York Post reported Friday a tester got a mock improved explosive device in his pants through security, including a pat-down. It led a congressman to call for a full security review.

The TSA says test items are "extremely hard to spot," not "a cartoonish bundle of dynamite with an alarm clock strapped to it." It says the reported slipping of a mock IED past screeners tested just one of 20 layers of security.