Speaking at a three-day international security conference in Singapore, Hagel on Saturday accused China of "destabilizing unilateral action" in pushing through its maritime territorial claims.

He said the United States would not remain a passive onlooker if international rules and standards were ignored.

"America will not look the other way when fundamental principles of the international orders are being challenged. We will uphold those principles," he told the Shangri-La Dialogue in Singapore.

"All nations of the region, including China, have a choice: to unite and recommit to a stable regional order, or to walk away from that commitment and risk the peace and security that has benefited millions of people throughout the Asia-Pacific, and billions of people around the world," he said.

He added that the US would maintain a strong military presence in the region.

China has reacted angrily to Hagel's comments, with the Deputy Chief of the General Staff of the People's Liberation Army, Wang Guanzhong, calling them "completely without basis, without reason."

Wang is scheduled to speak himself on Sunday.

Ongoing disputes

China is involved in territorial disputes with other countries in both the East and South China Seas, leading to tense relations with Japan, Vietnam and the Philippines in particular.

In a recent incident, Beijing's decision to set up an oil rig in part of the South China Sea also claimed by Vietnam has led to a series of clashes between the two nations in the waters around the rig.

China and Japan have also been at odds over the uninhabited Senkaku Islands - known as Diaoyu in China - in the East China Sea, which are under Japanese administration but are claimed by both. China's declaration of an air defense zone over a part of the sea that includes the disputed islands has further fueled tensions.

Hagel said the islands fall under the administration of the mutual defense treaty between the US and Japan, and that any change from Japanese control "should be done by international norms, not through intimidation and coercion."

Call for democracy

In his speech, Hagel also emphasized the importance of democratic development in the Asia-Pacific region.

In this connection, he urged the Thai army to release people detained during a coup earlier this month and to allow "free and fair elections."

His remarks come after the coup leader, General Prayuth Chan-ocha, said on television that elections are still more than a year away.

The Thai army seized power on May 22 following months of political unrest in the country, and detained senior politicians .

Hagel reiterated that the US was now reconsidering its military engagement and assistance with Thailand.

tj/hc (dpa, AFP, AP)