Republican senators pressed the Pentagon on Thursday to flex U.S. military muscle by sailing Navy ships within 12 miles of artificial islands Beijing is building to assert its territorial claims in the South China Sea.

Sen. John McCain, R-Ariz., chairman of the Senate Armed Services Committee, said the U.S. needs to go within the 12-mile limit to make it clear that the U.S. does not recognize China's claim that the islands are its territory.

"This is a dangerous mistake that grants de facto recognition of China's man-made sovereignty claims," McCain said at a committee hearing held ahead of the Chinese president's visit to the U.S. on Sept. 25.

While not violating international law, McCain said China sent its own naval vessels within 12 nautical miles of the Aleutian Islands as President Barack Obama concluded his recent visit to Alaska. The U.S. should assert its right of navigation "just as forcefully," McCain said.

U.S. ships haven't sailed within the 12-mile boundary since 2012, said David Shear, assistant secretary of defense for Asian and Pacific security affairs. Adm. Harry Harris, Jr., commander of U.S. Pacific Command, said the U.S. also has not conducted a direct fly-over of any of the lands and territories that China recently has reclaimed.

"I agree that the South China Sea is no more China's than the Gulf of Mexico is Mexico's," Harris said.

Senators peppered Harris and Shear with questions about whether the Pentagon has asked the White House for permission to sail within 12 miles of the manufactured islands and what the answer has been.

Asked for his military advice, Harris finally acknowledged that "I believe that we should be allowed to exercise freedom of navigation and maritime flight in the South China Sea against those islands." Harris said he was awaiting directions from his superiors.

Under further questioning, Shear refused to talk about the ongoing deliberations between the Pentagon and the White House, but he said that exercising freedom of navigation around the islands is just one option.

"Freedom of navigation alone won't stop" the Chinese activities, he said.

China has reclaimed about 3,000 acres in the South China Sea, triggering repeated objections from the U.S and allies.

Sen. Dan Sullivan, R-Alaska, pointed to Defense Secretary Ash Carter's public statement on Wednesday that the U.S. will not be deterred in ensuring freedom of navigation in the region.

"There should be no mistake: the United States will fly, sail, and operate wherever international law allows, as U.S. forces do all over the world," Carter said. "After all, turning an underwater rock into an airfield simply does not afford the rights of sovereignty or permit restrictions on international air or maritime transit."

Sullivan also said that he thought China was trying to provoke the United States when it moved five Chinese warships into the Bering Sea near Alaska at a time when Obama was visiting the state near the Arctic Circle.

Harris disagreed.

"My opinion is that they went into the Bering Sea to demonstrate their capability to operate that far North," Harris said.

"They were having an exercise with the Russians and I think the exercise was long-planned and then they decided to go into the Bering Sea. They were near there anyway and then they turned South and headed home. I think it was coincidental, but I don't know that for a fact."

Sullivan said he was convinced it was more of a provocation, saying "I'm not sure this administration would recognize provocation if it were slapped in the face."