The U.S. Navy sent a guided-missile destroyer within 12 nautical miles of artificial islands built by China in the South China Sea on Tuesday, a U.S. defense official said, in a challenge to China’s territorial claims in the area.

The official said the USS Lassen was sailing near Subi and Mischief reefs in the Spratly archipelago, features that were submerged at high tide before China began a massive dredging project to turn them into islands in 2014.

“The operation has begun … It will be complete within a few hours,” said the official, who spoke on condition of anonymity.

The mission would be the start of a series of challenges to China’s territorial claims in one of the world’s busiest sea lanes, another U.S. defense official said.

The second official earlier said the ship would likely be accompanied by a U.S. Navy P-8A surveillance plane and possibly P-3 surveillance plane, which have been conducting regular surveillance missions in the region.

Read more: http://www.reuters.com/article/2015/10/27/us-southchinasea-usa-idUSKCN0SK2AC20151027