Washington (AFP) - Asian countries are seeking to strengthen military ties with the United States in the face of Beijing's expansionist ambitions in the South China Sea, Pentagon chief Ashton Carter said Friday ahead of a regional visit that will not include a China stop.

"Almost all the nations there are asking us to do more with them... bilaterally and multilaterally," Carter told the Council on Foreign Relations think tank in New York, before he heads off on a trip next week that includes India and the Philippines.

"Indeed, in the South China Sea, China's actions are raising regional tensions," added Carter, who was invited to Beijing and accepted a visit sometime in the spring.

But the trip was shelved several weeks ago because of what a US defense official called a scheduling problem.

"Countries across the Asia-Pacific are voicing concern with militarization, and especially with China’s actions, which stand out in size and scope," Carter said.

He added: "That’s why many of those countries are reaching out anew to the United States to uphold the rules and principles that have allowed the region to thrive."

China lays claim to almost all of the contested South China Sea, which is important for international shipping and believed to hold valuable mineral and energy deposits.

Neighboring countries and Washington fear China could impose military controls over the entire South China Sea, and Beijing has in recent months built massive structures including radar systems and an airstrip over reefs and outcrops.

Carter reiterated the US line urging a diplomatic solution to ease tensions in the South China Sea, where the Philippines, a US ally, is among the claimants.

Ties between Washington and Beijing have been prickly over a range of issues, the South China Sea prime among them.

Bill Urban, a Pentagon spokesman, said officials were "actively looking" for Carter to visit China later this year.