BEIJING -- China on Wednesday suggested the United States, when talking about "freedom of navigation," make a distinction between commercial ships and warships.

Freedom of navigation for commercial vessels has never been obstructed in the South China Sea, said Foreign Ministry spokesman Lu Kang at a daily press briefing.

US assistant secretary of state for East Asia and the Pacific Daniel Russel said on Tuesday in Vietnam that freedom of navigation operations were important to smaller nations.

"If the world's most powerful navy can not sail where international law permits, then what happens to the ships of navy of smaller countries?" Russel told reporters.

The United States appears to advocate freedom of navigation for military vessels in the South China Sea, which is against international law, said Lu, noting that no other country in the world would even suggest such a thing.

According to the UN Convention on the Law of the Sea (UNCLOS), foreign vessels enjoy the right of innocent passage through territorial seas, but military vessels are not endowed with the same right, said Lu.

The United States refused to ratify the UNCLOS and introduced "freedom of navigation" operations in 1979. These operations have met with opposition from the very beginning, especially from smaller nations, he said.

"We hope the US will respect basic facts when talking about the feelings of smaller nations," he said, suggesting the United States sign and ratify the convention as soon as possible to give its words on international law more force.

China on Tuesday expressed "resolute opposition" to a US warship patrol in the South China Sea near Yongshu Jiao in the Nansha Islands.

The warship, USS William P. Lawrence, illegally entered Chinese waters near the islands on Tuesday without the permission of the Chinese government.