China's State Oceanic Administration (SOA) said on July 5 U.S. energy giant ConocoPhillips was responsible for an oil spill in the country's northern sea area.

The leaks, which occurred in June in the Penglai 19-3 oilfield in the Bohai Bay, contaminated an area of 840 square km and caused "a certain level" of damage to the nearby ocean environment, said the administration.

The field is being drilled by ConocoPhillips China, a subsidiary of ConocoPhillips, under a joint development agreement with the China National Offshore Oil Corp., the country's largest offshore oil producer.

SOA said oil seepage was first reported to its North China Sea Branch by ConocoPhillips on June 4, with another incident reported on June 17. The leakage was brought under control by June 21.

The administration said the seepage from platform-B was caused by drilling using hydraulic pressure, while the leak from platform-C was due to a surge in the well.