China's maritime authority said Wednesday that it has established a special team to sue US oil firm ConocoPhillips over the oil spills in China's north Bohai Bay, and the team is close to complete the ecological investigation.

Spilled oil can still be seen on the surface of the water near the affected area in North China's Bohai Bay, on August 22, 2011. The oil spills near Platform C at Penglai 19-3 oil field were first detected on June 4. [Xinhua]?

Fang Jianmeng, head of the North China Sea branch of the SOA, said Tuesday that he has been named as the leader of the special team, which has collected enough evidence of the oil pollution after completing four rounds of investigations.

Fang said the branch has launched environmental damage assessment survey to the 16 provinces and cities around Bohai Bay since June and will be able to offer legal documents for the lawsuit.

The State Oceanic Administration (SOA) said last week that it would file a lawsuit demanding compensation after assembling a team of lawyers. Now four legal teams have been selected from 49 firms applied for the lawsuit, according to Economic Observer.

The branch stated the spills from ConocoPhillips' Penglai 19-3 oil field has polluted 5,500 square km of the bay and 870 square km have been seriously polluted, quoted by Xinhua news agency.

The SOA has given an ultimatum to ConocoPhillips– by Aug 31 the sources of the leak must be sealed and a thorough and complete inspection must be done to eliminate the potential risk of another oil spill.

The company said in a statement on Monday that it had cleaned up 99 percent of the mineral oil-based drilling mud near Platform C at Penglai 19-3 oil field. They will hand over the assessment report to the SOA on Aug. 31.

However, the company's statement raised queries among environmental experts and lawyers.

"Currently, it is not clear that all the oil spill sources have been discovered since most of them are 30 to 40 meters under the sea surface and are difficult to see," Wang Yamin, a marine professor at Shandong University, told the portal website Sina on Tuesday.