The commander of U.S. forces in the Pacific said Tuesday that China is seeking control of East Asia, comments that could further inflame tensions between the two world powers.

Adm. Harry Harris, Jr., told a congressional hearing that China's construction and military facilities are changing the operational landscape in the disputed South China Sea, where Beijing has undertaken a massive land reclamation effort to press its sweeping territorial claims.

Harris told the Senate Armed Services Committee that China is militarizing the South China Sea, "and you have to believe in a flat earth to think otherwise."

Asked what about the strategic goal of China's military buildup in the region, Harris told lawmakers: "I believe China seeks hegemony in East Asia." When asked if that meant regional control, Harris concurred.

His comments are likely to anger Beijing, whose top diplomat is due to meet with Secretary of State John Kerry in Washington later Tuesday at a fraught time in relations.

The two sides have been trading accusations over militarization in the South China Sea, an important thoroughfare for world trade where six Asian governments have competing territorial claims. The U.S. is not a claimant but says it has an interest in maintaining peace and stability there, and freedom of navigation and commerce.

The rhetoric has heated up since it emerged last week that China had Beijing deployed anti-aircraft missiles on a disputed island in the Paracels chain. Then on Monday, a U.S. think tank reported that China has built new radar facilities in the Spratly Islands, which lie further south.

China denies it has aggressive intent. Its Foreign Ministry on Tuesday reasserted Beijing's right to develop its South China Sea island outposts, saying it has sovereignty over them.

"China is exercising the right of self-preservation that every country enjoys according to international law, which is beyond reproach," Foreign Ministry spokeswoman Hua Chunying told reporters in Beijing.

Another source of tensions with the U.S. has been differences over how to respond to North Korea's latest nuclear test and rocket launch. It's been seven weeks since the nuclear test and the U.S. and China still haven't agreed on how to censure Pyongyang.

While China has joined in the international criticism, it has balked at imposing the kind of tough economic sanctions that the U.S. wants, fearing it could threaten the stability of North Korea, a neighbor and traditional ally of Beijing.

In the meantime, the U.S. has taken tougher steps of its own, tightening sanctions and announcing it will hold formal talks with its close ally South Korea on deploying a missile defense system that China fears could be used against it as well North Korea.

Harris said it was "preposterous" that China would try to "wedge itself" between South Korea and the U.S. for a missile defense system designed to defend Americans and Koreans on the Korean Peninsula.

He said if China is truly concerned, it should intervene with North Korea and convince it to quit its cycle of provocations.

Kerry and Wang are expected to discuss Tuesday how to reach a compromise over a U.N. Security Council resolution against the North Korea, and also the mounting differences over the South China Sea -- issues that have put a growing strain on efforts to forge a cooperative relationship.

The Obama administration faces congressional pressure to step up its efforts to counter China.

Republican Sen. John McCain said that China is behaving like a "bully" in the Asia-Pacific. He said the administration's "risk aversion" has failed to prevent China's coercive behavior. He called for more freedom of navigation operations and possibly boosting the U.S. military posture in the region.

A couple of U.S. Navy operations close to disputed land since October have already riled Beijing.