Islands at the center of a territorial row between Japan and China are covered by a military protection accord between Washington and Tokyo, US Defense Secretary Chuck Hagel said Monday.

"The United States does not take a position on the ultimate sovereignty of the islands, but we do recognize they are under the administration of Japan and fall under our security treaty obligations," Hagel said at a news conference with his Japanese counterpart Itsunori Onodera.

Hagel's comments came amid rising tension over the uninhabited islands known in Japan as the Senkakus and in China as the Diaoyus.

On April 23, Japan's prime minister vowed to "expel by force" any Chinese landing on the islands after a flotilla sailed into the disputed waters in the East China Sea.

The Chinese flotilla was the biggest to do so in a single day since Japan nationalized part of the island chain -- which is surrounded by rich fisheries and believed to harbor vast natural resources below the seabed -- in September.

Calling the dispute a key regional security challenge, Hagel said it "must be resolved peacefully and cooperatively between the parties involved."

Washington "opposes any unilateral or coercive action that seeks to undermine Japan's administrative control," he said, in reference to the recent Chinese actions.

"Any actions that could raise tensions or lead to miscalculations affect the stability of the entire region."

In the talks with Hagel, Onodera said he "explained Japan's basic position that the islands are clearly an inherent part of the territory of Japan in light of historical facts and based upon international law, and that Japan is determined to protect its land, water and air."

Turning to North Korea, the Pentagon chief said the isolated country's "provocative behavior" was "the most obvious threat to stability in the region."

"Minister Onodera and I agree that continued close coordination between US and Japanese forces will be essential for monitoring and responding to any further provocations, particularly cooperation on missile defense," he added.

On that front, Hagel said progress had been made on plans to deploy a second TPY-2 radar to Japan.

Hagel also confirmed the deployment of a second squadron of MV-22 Osprey aircraft to Japan this summer.