Mitsui added it is carefully studying the bill and will continue to talk to BP.
Mitsui, which owns a 10 percent stake in the well through its unit Mitsui Oil Exploration, and Canada's Anadarko Petroleum Corp, which has 25 percent, said last month they will not set aside money for cleanup costs along the Gulf Coast, arguing that it is BP's responsibility.
BP has a 65 percent interest in the well and is its exclusive operator, they said. The oil leakage killed 11 people and caused the worst environmental disaster in U.S. history.
Mitsui's first-quarter net profit jumped 79 percent to 102.5 billion yen ($1.2 billion), and it stuck to its 320 billion yen profit forecast for the year to March, which would be double last year's result.
Mitsui said it is difficult at this point to estimate the oil spill's impact on its earnings.
Shares of Mitsui & Co were up 5 percent at 1,164 yen, outperforming a 1.1 percent rise in the benchmark Nikkei 225.
(Additional reporting by Abhinav Sharma in Bangalore; Editing by Edwina Gibbs)