WASHINGTON (AFP) - The United States criticised China as provocative Monday after its coast guard tried to block a Philippine vessel that was rotating troops in the tense South China Sea.

The attempted Chinese blockade, which led to a two-hour standoff with the Philippine ship, is "a provocative and destabilizing action," State Department deputy spokeswoman Marie Harf told reporters.

Harf said that the Philippines had permission to resupply troops to the remote reef, the Second Thomas Shoal, because it has kept a naval presence there since before a 2002 declaration of conduct in the South China Sea.

"As a treaty ally of the Republic of the Philippines, the United States urges China to refrain from further provocative behavior by allowing the Philippines to continue to maintain its presence at Second Thomas Shoal," she said.

The incident was the latest in the South China Sea, where China claims a vast area that overlaps with several neighbors' claims.

On March 9, China successfully turned away a similar resupply boat from the Philippines.

The United States has been warning China against taking more drastic action in the South China Sea after it declared an air defense identification zone in November over much of the East China Sea, including islands administered by Japan.