The financial cost of tackling the oil spill in the Gulf of Mexico, the worst in U.S. history, now stands at $990 million, BP said on Tuesday as it prepared for a new attempt to control the flow of oil this week.

London-based BP will try to place a containment cap on top of a lower marine riser package (LMRP) later this week after two previous attempts to plug or contain the well failed.

The company cautioned that the time frame for deployment of the LMRP cap could be delayed as the catastrophe enters its 43rd day and the hurricane season starts officially on Tuesday.

BP said it continues to drill two relief wells as part of a longer term plan to control the leak, and that drilling at a second well had resumed on May 30 after a temporary suspension. The wells are expected to be completed in August.

The total financial cost of the response in the six weeks since a rig explosion killed 11 workers and unleashed oil from a well head one mile down stands at $990 million, up from a $930 million estimate on May 28, BP said.

(Reporting by Sarah Young; editing by Paul Hoskins)