A Chinese warship confronted an Indian naval vessel in waters off Vietnam and demanded its identity, the Financial Times said on Thursday, amid regional concern over Beijing's maritime assertiveness.
The London-based newspaper reported that five people familiar with the incident said it occurred in international waters shortly after India's amphibious assault ship INS Airavat completed a scheduled port call in Vietnam.
Delhi confirmed contact was made with its ship, but rejected the suggestion of a "confrontation".
On July 22 after sailing 45 nautical miles off Nha Trang, the INS Airavat was called on an open radio channel by someone identifying himself as the "Chinese Navy", the Indian government said in a statement.
"You are entering Chinese waters," the radio caller said, according to the statement. It added that no ship or aircraft was visible from the Indian vessel, which proceeded as scheduled.
"India supports freedom of navigation in international waters, including in the South China Sea, and the right of passage in accordance with accepted principles of international law. These principles should be respected by all," Delhi said.
A series of Chinese actions in the South China Sea have caused nervousness among regional neighbours -- particularly Vietnam and the Philippines.
China says it has sovereignty over essentially all of the South China Sea, a key global trading route, where its professed ownership of the potentially oil-rich Spratly archipelago overlaps with claims by Vietnam, the Philippines, Taiwan, Brunei and Malaysia.
Vietnam and China have a separate long-standing dispute over the more northerly Paracels archipelago.
The INS Airavat visited Nha Trang in south-central Vietnam and the northern port of Haiphong in the second half of July.
Vietnam's foreign ministry said it had no information about the incident, while China's foreign ministry spokesman said he had queried the defence ministry but had not yet received a response.
A source familiar with the incident told AFP it was "a typical Chinese approach", adding that Beijing's enforcement vessels try to assert "that this is their territory and what are you doing in their territory?".
In recent months, the Philippines and Vietnam have objected to what they said was Chinese harassment of oil exploration vessels and fishermen in the South China Sea.
US Secretary of State Hillary Clinton in July condemned acts of "intimidation" in the waters, where it says it has a national interest in free navigation.
A Pentagon report on Wednesday last week said China is increasingly focused on naval power, as it places a growing priority on securing strategic shipping lanes and mineral-rich areas in the South China Sea.
Chinese leaders have insisted their military modernisation programme is aimed solely at "self-defence