Pentagon chief Chuck Hagel on Sunday warned China against unilateral action to resolve territorial disputes with its neighbours, drawing a parallel with Russia's incursion in Ukraine as he announced two more warships would be sent to Japan.
Seeking to reassure Washington's longtime ally Japan, Hagel's remarks and promise of more missile defence ships came as Tokyo faces a tense row with Beijing over islands in the East China Sea.
"All nations deserve respect, no matter how large or how small," Hagel said during a visit to Tokyo.
"I think we're seeing some clear evidence of a lack of respect, and coercion and intimidation with ... what the Russians have done in Ukraine," he told a news conference with his Japanese counterpart, Itsunori Onodera.
Countries had to speak up and reject such a blatant violation of international law, said Hagel, referring to Russia's annexation of Ukraine's Crimean peninsula.
And in a veiled reference to China and its territorial arguments with Asian neighbours, Hagel said smaller countries had the same sovereign rights as larger states.
"You cannot go around and redefine boundaries, violate territorial integrity and sovereignty of nations by force, coercion and intimidation -- whether it's in small islands in the Pacific, or large nations in Europe," Hagel said.
"So I want to talk to our Chinese friends about this," said the defence secretary, who departs for Beijing on Monday.
His comments underscored a tougher line by the US government on China's approach to territorial claims in the South China Sea and the East China Sea, after some Southeast Asian countries accused Beijing of intimidatory tactics.
As "a great power," China has "great responsibilities," Hagel said.
A topic Hagel plans to raise with the Chinese this week is "respect for their neighbours," he said.
"Coercion, intimidation is a very deadly thing. It leads only to conflict," he said.
In Tokyo, Hagel unveiled plans to send two more Aegis missile defence warships to Japan by 2017, citing "Pyongyang's pattern of provocative and destabilising actions."
The US ships would join five missile defence vessels already stationed in the area, and were part of an American strategic "rebalance" to the Asia-Pacific, officials said.
Japan has deployed its own Aegis missile defence ship to the Sea of Japan (East Sea) in recent days, after North Korea last month test fired two medium-range ballistic missiles.
Tokyo has reportedly ordered its forces to destroy any North Korean ballistic missiles that pass through its airspace.
Hagel's announcement follows the deployment of a second early warning US radar to Japan, P-8 maritime surveillance aircraft and plans to bring unmanned Global Hawk drones to the country.
Although Hagel said the US ships were being sent to help counter the threat posed by North Korea, the move also carried symbolic weight amid Japan's tense stand-off with China over islets in the East China Sea.
Hagel reiterated that Washington stood by its mutual defence treaty with Japan, saying it applied to the disputed islands in the East China Sea, where Beijing and Tokyo are locked in a bitter argument.
"We take seriously American's treaty commitments, and we strongly oppose any unilateral coercive action that seeks to undermine Japan's administrative control," Hagel said.
The Pentagon chief, who is due to fly to China Monday for a three-day visit, called for "a peaceful resolution" of the disagreement and said "America has no stronger ally or better friend in this region than Japan."
Tokyo scrambled military aircraft last month after three Chinese planes flew near Japanese airspace, the latest confrontation in the East China Sea dispute.
The islands are administered by Japan, which calls them Senkaku Islands, but are referred to as the Diaoyu Islands by China.
Chinese ships and planes have been seen off the disputed islands numerous times since Japan nationalised them in September 2012, sometimes within the 12 nautical-mile territorial zone.