The USS Preble and USS Chung Hoon traveled within 12 nautical miles of the Gaven and Johnson Reefs in what the Navy calls a freedom of navigation operation "in order to challenge excessive maritime claims and preserve access to the waterways as governed by international law," said Seventh Fleet spokesperson Cmdr. Clay Doss.
The operation comes amid heightened tensions between the U.S. and China over a possible trade deal. According to Reuters, which was first to report the passage, the Chinese foreign ministry responded by saying the U.S. ships entered the area without permission and were told to leave.
While the Navy carries out freedom of navigation operations around the world, the ones directed at claims made by China draw the most attention with the last transit through the South China Sea occuring in February. By sailing within the international territorial limit of 12 nautical miles, the operations stress that the waters off the artificial islands are international waters.
China is one of several nations that claim reefs and islets in the South China Sea, but in recent years has militarized island chains. In 2018, China placed anti-ship cruise missiles and long-range surface-to-air missiles on the contested Spratly Islands, according to a recent Pentagon report.
"All operations are designed in accordance with international law and demonstrate that the United States will fly, sail and operate wherever international law allows. That is true in the South China Sea as in other places around the globe," Doss said, adding that freedom of navigation operations are "not about any one country, nor are they about making political statements."
ABC News' Luis Martinez contributed to this report.