WASHINGTON - The Obama administration on Friday warned China against further moves to tighten control over a disputed section of the South China Sea, as tensions rose in the flash point region.

In a statement, the State Department cautioned China about its addition of a military garrison and civilian officials near the contested Scarborough Reef and its use of barriers to deny access to foreign ships.

These moves "run counter to collaborative diplomatic efforts to resolve differences and risk further escalating tensions in the region," said the statement, issued early Friday morning and attributed to Patrick Ventrell, the acting deputy spokesman.

Six countries have complex competing claims to the region's water and islands, which are rich in fish, oil and gas and other resources.

China's recent moves over the Scarborough Reef have ruffled feathers in several nations, including Vietnam, Japan and the Philippines. There also have been reports that China is preparing to invite oil company bids for energy exploration in the area.

Countries in the region have been trying to work out a method for peacefully arbitrating their claims through a leading regional body, the Association of Southeast Asian Nations, and have urged states not to take any provocative actions.

The U.S. statement appeared to be a sign to Southeast Asian countries that the administration continues its close watch on developments in the region. But one analyst cautioned that by singling out China at a time when several nations have been pushing claims, the Obama administration may confirm Chinese fears that it is strengthening security ties in Southeast Asia to limit the expansion of Chinese power.

"It's very likely that China will read this as unnecessary, and confirming its concerns that the U.S. is actively seeking to line up with Southeast Asia against it," said Kenneth Lieberthal, a China specialist at the Brookings Institution and a former Clinton administration official.

Administration officials announced last year that they were shifting their foreign policy attention more to East Asia and have announced a series of steps to reinforce security ties with Vietnam, the Philippines, Australia and other countries.