New Delhi, Aug. 27: State-owned refiner ONGC has received a one-year extension to explore oil in a Vietnam block in the contested waters of South China Sea.

In a regulatory filing, ONGC today said its overseas investment arm, ONGC Videsh Ltd (OVL), had applied for the extension to Vietnam's national oil company PetroVietnam on May 28. "In response to OVL's request, PetroVietnam has granted extension of the block up to June 15, 2016," it said.

OVL had applied for a third extension of the licence for deep-sea block 128 to maintain India's strategic interest in the South China Sea.

"OVL has not found any hydrocarbon in the block but will continue operations in line with India's strategic and diplomatic interest in the region. The renewal is being seen as India's attempt to assert its presence in the region," energy analysts said.

The South China Sea, which is supposed to have vast oil and gas reserves, is one of the world's busiest shipping lanes with about five trillion dollars of trade and about 50 per cent of the global oil tanker shipments passing through it every year.

China lays its claim over 90 per cent of the South China Sea.

OVL had signed a production-sharing contract for the 7,058-square-km block 128 in offshore Phu Khanh Basin of Vietnam on May 24, 2006.