"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 joint news conference with his Japanese counterpart, Itsunori Onodera.
Countries had to speak up and clearly reject such a blatant violation of international law, said Hagel, referring to Russia's annexation of Ukraine's Crimean peninsula.
"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 tomorrow.
Hagel's blunt remarks came as he reaffirmed Washington's military alliance with Tokyo and announced the deployment of two more ballistic missile defence ships to Japan.
Hagel reiterated that Washington stood by its mutual defence treaty with Japan, saying it applied to disputed islands in the East China Sea, where Beijing and Tokyo are locked in a bitter argument.
"We take seriously America's treaty commitments, and we strongly oppose any unilateral coercive action that seeks to undermine Japan's administrative control," Hagel said.
The Pentagon chief called for "a peaceful resolution" of the disagreement and said: "America has no stronger ally or better friend in this region than Japan."
The islands are administered by Japan, which calls them the Senkaku Islands, but which China refers to as the Diaoyu Islands.
Chinese government 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.
