Japanese trading house Mitsui & Co., which owns a stake in the Gulf of Mexico oil well that caused the world's worst offshore oil spill, said it has received a $1.9 billion bill from BP towards the cleanup, four times bigger than a bill sent three months ago.

Mitsui reiterated it would withhold payment while it continues to examine the issue.

"We'll withhold a decision until the cause of the spill and how the cost is shared among stakeholders become clear," Junichi Matsumoto, executive vice president at Mitsui, told a news conference.

"We asked BP for more details as it was unclear how they calculated the bill, but there was no response as of the end of October."

Matsumoto said the Mitsui group is subject to 154 lawsuits in the U.S.
News of the demand comes as Mitsui, Japan's second-biggest trading house, reported net profit for the April-September first half of 183.23 billion yen ($2.28 billion), 2.5 times more than a year earlier, on strong sales of iron ore and other commodities.

Matsumoto said the company had not booked any cleanup costs in its earnings as of the end of September.

Millions of gallons of oil poured into the Gulf of Mexico in the worst environmental disaster in U.S. history, which began in April when a BP rig exploded and sank off the coast of Louisiana. The well was capped in July.

Mitsui's unit, Mitsui Oil Exploration Co., holds a 10 percent stake in the ruptured oil well.

Several investigations into the cause of the spill are under way, including those by the U.S. government and Mitsui. The first result is expected as early as June next year, Matsumoto said.

BP has been selling assets to raise cash to pay for the cleanup and compensate victims.

Shares of Mitsui ended 0.8 percent lower at 1,244 yen compared with a flat broader market.