Over the weekend, Littoral Combat Ship USS Montgomery (LCS-8) conducted a freedom of navigation operation through waters near the Spratly Islands claimed by China, Taiwan and Vietnam, the Navy said.

Montgomery, an Independence-variant LCS, steamed past the Spratly Islands in the South China Sea on Saturday, according to a statement released by U.S. 7th Fleet. Montgomery’s FONOP is believed to be the first of 2020 in the South China Sea.

China, Vietnam, Taiwan, Malaysia, Brunei and the Philippines claim sovereignty over some or all of the islands in the chain.

Also, China, Taiwan and Vietnam all state they require foreign military vessels to either ask permission or provide advance notice before sailing by the islands, a requirement Navy officials and most maritime experts say is contrary to international law.

“The unilateral imposition of any authorization or notification requirement for innocent passage is not permitted by international law, so the United States challenged these requirements,” the 7th Fleet statement said. “By engaging in innocent passage without giving notification or asking for permission, the United States challenged the unlawful restrictions imposed by China, Vietnam, and Taiwan. The United States demonstrated that innocent passage may not be subject to such restrictions.”

Under the U.N. Law of the Sea Convention, a foreign warship can pass within 12 nautical miles of a territorial claim as long as it takes a direct route and doesn’t conduct military operations.

Chinese officials were quick to issue a response complaining about the U.S. operation in a region they consider part of China’s territorial waters. The Chinese military monitored Montgomery’s passage and warned the ship to leave the region, Senior Col. Li Huamin, a spokesperson for the People’s Liberation Army (PLA) Southern Theater Command, said in a statement on Tuesday. China deployed naval and air forces to track Montgomery.

“The Chinese military is determined to safeguard national sovereignty and security as well as maintain peace and stability in the South China Sea, no matter what tricks are played by U.S. ships,” Li said.

In November, USS Gabrielle Giffords (LCS-10) conducted a FONOP past the Spratly Islands, as part of the ongoing U.S. effort to uphold freedom of navigation through the region.

“The United States upholds freedom of navigation as a principle,” the 7th Fleet statement said. “The Freedom of Navigation Program’s missions are conducted peacefully and without bias for or against any particular country. These missions are based in the rule of law and demonstrate our commitment to upholding the rights, freedoms, and lawful uses of the sea and airspace guaranteed to all nations.”

The following is the full statement from U.S. 7th Fleet about the freedom of navigation operation conducted by USS Montgomery (LCS-8):

On Jan. 25, a U.S. warship asserted navigational rights and freedoms in the Spratly Islands, consistent with international law. This freedom of navigation operation (“FONOP”) upheld the rights, freedoms and lawful uses of the sea. Independence-variant littoral combat ship USS Montgomery (LCS-8) challenged the restrictions on innocent passage imposed by China, Vietnam, and Taiwan.

China, Vietnam, Taiwan, Malaysia, Brunei and the Philippines each claim sovereignty over some or all of the Spratly Islands. China, Vietnam, and Taiwan purport to require either permission or advance notification before a foreign military vessel engages in “innocent passage” through territorial seas. Under international law as reflected in the Law of the Sea Convention, the ships of all States – including warships – enjoy the right of innocent passage through territorial seas. The unilateral imposition of any authorization or notification requirement for innocent passage is not permitted by international law, so the United States challenged these requirements. By engaging in innocent passage without giving notification or asking for permission, the United States challenged the unlawful restrictions imposed by China, Vietnam, and Taiwan. The United States demonstrated that innocent passage may not be subject to such restrictions.

U.S. forces routinely conduct freedom of navigation assertions throughout the world. All of our operations are designed to be conducted in accordance with international law and demonstrate that the United States will fly, sail, and operate wherever international law allows – regardless of the location of excessive maritime claims and regardless of current events.

The United States upholds freedom of navigation as a principle. The Freedom of Navigation Program’s missions are conducted peacefully and without bias for or against any particular country. These missions are based in the rule of law and demonstrate our commitment to upholding the rights, freedoms, and lawful uses of the sea and airspace guaranteed to all nations.

Freedom of navigation operations in the South China Sea are a part of daily operations of U.S. military forces throughout the region.