Dutch authorities say beefed-up security measures at Amsterdam's Schiphol Airport are being scaled back following investigation of an unspecified threat.

The country's National Coordinator of Counterterrorism and Security says in a statement that some of the extra measures, which included military police checking cars approaching the airport to drop off passengers, will end Thursday evening, just under three weeks after they were introduced.

The counterterror coordination office says "further investigations have led to the conclusion that some of the extra measures are no longer necessary."

The move comes amid busy days at the national airport as the summer vacation period draws to a close.

Since March 2013, the threat level in the Netherlands has been at "substantial," the second highest on a five-step scale.