Shrugging off Chinese warnings, India's state-run oil firm ONGC said on Friday it would press ahead with long-term partner Vietnam in exploring the disputed South China Sea for oil.

The plans have stoked concerns that the exploration could exacerbate tensions between fast-growing neighbours China and India, who fought a brief, bloody war in 1962 over their disputed Himalayan border.

China has repeatedly said it has "indisputable sovereignty" over essentially all of the South China Sea, a key trading route, and that Beijing is opposed to any country engaged in oil and gas exploration there without its permission.

But India insists the area ONGC wishes to explore is well within Vietnam's territorial waters.

"We will proceed with drilling at our block (in the South China Sea) on a schedule established according to our technical convenience," a senior Oil and Natural Gas Corp (ONGC) executive told AFP, asking not to be named.

He added India's foreign ministry had told ONGC the area where the oil firm wished to explore was "very much inside Vietnam's territory."

ONGC is expected to resume drilling next year at one of its two blocks in the mineral and fuel-rich South China Sea, where Vietnam, the Philippines, Taiwan, Malaysia and Brunei also have claims.

The Indian statement came a day after Chinese foreign ministry spokeswoman Jiang Yu said oil and gas exploration activities carried out by a foreign company without the approval of China were illegal and invalid.

India, worried about encirclement by Chinese interests in the South Asian region, has been cooperating with Vietnam since the early 1990s as part of its "Look East policy" aimed at expanding ties with its eastern neighbours.

"This (oil exploration) is one important area of cooperation with Vietnam and we would like this area of cooperation to grow," India's foreign affairs spokesman Vishnu Prakash said earlier this month.

India's oil exploration projects in two Vietnamese blocks in the South China Sea were in line with "international laws," he added.

But the Chinese state-run Global Times, in a hard hitting editorial, has said Vietnam's efforts to bring in foreign companies to explore for oil amount to a "serious political provocation".

"China does not like being defied," Indian defence analyst Rahul Bedi told AFP.

At the same time, he said, India "does not yet have the military capability if it comes to a confrontation in the South China Sea on these oil blocks."

A Chinese warship was reported several weeks ago to have confronted an Indian naval vessel in waters off Vietnam and demanded its identity amid regional concern over Beijing's growing maritime assertiveness.

New Delhi has confirmed contact was made with its ship, but has rejected the suggestion of a confrontation.

Meanwhile the Philippines said Friday it had made headway in its bid to form a united front with its Southeast Asian neighbours against what it calls China's "illegal" grab of most of the South China Sea.

A meeting of delegates from Association of Southeast Asian Nations agreed that the UN Convention on the Law of the Sea should be the framework to resolve territorial disputes, Philippine Foreign Undersecretary Esteban Conejos said.

The delegates also endorsed an interim Philippine plan to ease tensions, which calls for identifying disputed areas, Conejos said.