An oil leak last month from China's?eastern?offshore oilfield was the fault of US energy giant ConocoPhillips, government officials said Tuesday,?and?warned the pollution will have a "long-term impact" on the marine environment.

A staff worker from the?State Oceanic Administration is taking the oil samples. [titan24.com]

The leak from platforms B and C of the Penglai 19-3 oilfield in the Bohai Bay, which started on June 4 and June 17 respectively, polluted 840 square kilometres of water, and ConocoPhillips China (COPC) should be held accountable for the incidents, the State Oceanic Administration (SOA) said yesterday.

Earlier reports said dead fish had been found near the site of the spills from the Penglai 19-3 field, though it has not been confirmed whether the deaths were caused by oil.

"There is still a small leak, but the spill is under control and the cleanup work is almost finished," Li Xiaoming, director of the department of marine environment protection at the SOA, said at a news conference. After an investigation that lasted just short of a month, the SOA has finished a preliminary assessment of the environmental impact.

"But as the impact is long-term and complicated, further investigation and assessment are still ongoing," Wang Bin, deputy director of the SOA's marine environment protection department, said.

The news conference was the first formal one held after the oil leak on June 4, which was first made public on Sina Weibo, a popular micro blog site, on June 21.

The Penglai 19-3 field has five production platforms, with total daily production of roughly 160,000 barrels.

ConocoPhillips has a 49 percent stake in the project while China's CNOOC Ltd has the remainder.

The two companies remained silent about the oil leak until Southern Weekend reported the spills on June 30. A joint news conference will be held?on Wednesday in Beijing to further brief the media about the incident.

Experts criticized the two companies for withholding the information from the public and called for stricter law enforcement on environmental protection.

Wang said that COPC faces a fine of 200,000 yuan ($29,850).