London, June 20 (IANS) Troubled British oil firm BP is preparing to sue Anadarko, one of its partners in the collapsed Gulf of Mexico oil rig, accusing it of "shrinking responsibilities" over sharing the clean-up cost of the oil spill.

BP is preparing legal action against Anadarko, which has 25 percent stake in the leaking oil well, after the company said BP's behaviour revealed "gross negligence" and that the accident was preventable, a British daily reported Sunday.

A senior BP source told The Sunday Telegraph that Anadarko was "shirking its responsibilities", not accepting its liabilities and that legal action in the US was now likely to follow.

Anadarko has already refused to share the clean-up cost. BP has already sent the company one demand for payment but, it was yet to receive any costs for the multi-billion ­dollar clean-up operation, the BP source said.

"The mounting evidence clearly demonstrates that this tragedy was preventable and the direct result of BP's reckless decisions and actions," said Jim Hackett, Anadarko's chief executive. "BP's behaviour and action is likely represent gross negligence or wilful misconduct".

Mitsui, the 10 percent owner of the well, has made no decision on whether to admit liability for its share of costs, but is likely to join Anadarko in its refusal to contribute. BP could then also take legal action against that company as well, the daily said.

The deepening row over the costs followed a call from US Congressman Edward Markey, saying Anadarko and Mitsui should be held accountable and set aside money to pay a share of claims tied to the spill. "They cannot escape responsibility," he said.

As the estimates for the total bill of the accident rose to between $30bn and $100bn, BP is understood to be adamant that the American and Japanese companies contribute their share. Their role in the well was purely financial and they had no operational responsibility.

However, a BP spokesman said the company strongly disagreed with Anadarko's claims.

"These allegations will neither distract the company's focus on stopping the leak nor alter our commitment to restore the Gulf coast," said BP's chief executive officer, Tony Hayward.

"Other parties besides BP may be responsible for costs and liabilities arising from the oil spill, and we expect those parties to live up to their obligations".

BP has established a $20 billion fund to meet environmental compensation claims, but did not have discussions with its partners about how they would contribute.

"Although we have not been involved in any way with the White House or BP in the process, we are pleased that BP has agreed to establish a $20bn escrow fund," said John Christiansen, an Anadarko spokesman.

"We believe this action by BP is consistent with their ­continued message that they will pay all legitimate claims."

A Mitsui spokesman said: "With regard to the issue of the escrow account, drawing an immediate conclusion about the underlying matters at hand would be premature."