India and Vietnam have agreed to expand oil exploration projects in the disputed South China Sea.

A total of eight agreements -- covering areas including energy, defense and education -- were signed Wednesday by the two countries as Nguyen Phu Trong, general secretary of the Vietnamese Communist Party, wrapped up his visit to India.

Under one agreement, Vietnam offered India's ONGC Videsh Ltd., known as OVL, an offshore block for continued oil and gas exploration in the South China Sea. OVL is already involved in a joint venture with Vietnam Oil and Gas Group, or PetroVietnam, in three oil blocks close to the disputed Spratly Islands.

PetroVietnam and OVL also signed an agreement for joint exploration, development and production of petroleum resources for new investments by OVL in oil and gas blocks in Vietnam.

India and Vietnam had not yet disclosed specific terms of those agreements, but they are likely to rattle China.

China maintains it has sovereignty over all the South China Sea, while Vietnam asserts competing claims over parts of the sea, including the Spratly Islands. The disputed waters are also claimed in whole or in part by the Philippines, Taiwan, Brunei and Malaysia.

"Both India and Vietnam belong to a region that holds enormous potential but also many challenges. We have a strong convergence of interests in working together and with others in the region, for a stable, peaceful and prosperous Asia," Press Trust of India reported Indian Prime Minister Manmohan Singh, standing with the Vietnamese leader, told reporters in New Delhi Wednesday.

In an interview with PTI Monday on the eve of his arrival to India, Nguyen said he appreciated India's "constructive role" in the disputed South China Sea region.

Beijing has called for India to halt its oil and gas exploration, saying that it should respect China's sovereignty.

"China opposes unilateral exploration and development of oil and gas in contested waters of the South China Sea. We hope relevant countries can respect China's claim, position and rights and interests, and respect and support efforts made by countries in the region to solve disputes through bilateral negotiations," PTI quoted China's Foreign Affairs Ministry as having said.

But Vietnam has argued India has the right to pursue oil exploration in the South China Sea because the area is within Vietnam's exclusive economic zone.

The South China Sea's oil reserves are estimated to be 23 billion-30 billion tons, China's Ministry of Land and Resources says.

Also during the Vietnamese leader's visit, India's Tata Power signed an agreement with the Vietnamese government to set up a 1,320 megawatt thermal power-generating plant in Vietnam.