The U.S. Senate on Thursday unanimously approved an amendment to the 2013 National Defense Authorization Act that is designed to counter attempts by China to challenge Japan's administration of the Senkaku Islands but sidesteps the question of who has ultimate sovereignty over the disputed territory.

The amendment, offered by Jim Webb, a Virginia Democrat, states U.S. opposition to any efforts to coerce, threaten to use force or use force to resolve territorial issues. It concludes by reaffirming the commitment of the U.S. to the defense of territories under the administration of Japan.

"The peaceful settlement of territorial and jurisdictional disputes in the East China Sea requires the exercise of self-restraint by all parties in the conduct of activities that would complicate or escalate disputes and destabilize the region, and differences should be handled in a constructive manner consistent with universally recognized principles of customary international law," the amendment says.

"While the United States takes no position on the ultimate sovereignty of the Senkaku Islands, the United States acknowledges the administration of Japan over the Senkaku Islands. The unilateral actions of a third party will not affect United States acknowledgement of the administration of Japan over the Senkaku Islands," it adds.

"Over the past several years, China has taken increasingly aggressive actions to assert its claim over the Senkaku Islands in the East China Sea and in a broad expanse of the South China Sea," Webb said.