"The Indianapolis Motor Speedway has a comprehensive security plan for all of its events, created with full cooperation from federal, state of Indiana and local law enforcement authorities," the statement said.

"A thorough review of that process is underway with all appropriate authorities."

Organizers said a "full complement of law enforcement personnel will be on hand" for the race and expected everything to proceed as planned.

"The Indianapolis Motor Speedway expects all 11 Formula One teams to compete at this event with their regular drivers, and planning and logistics for the event continue on schedule," they added.

"Every top official involved with the organization of Formula One, including FIA (International Automobile Federation) President Max Mosley and Bernie Ecclestone, has indicated that the U.S. Grand Prix will continue as scheduled," said Tony George, Indianapolis Motor Speedway President.

The race, on September 30, had been in doubt after last week's air attacks on New York and Washington.

Some drivers, including German Ralf Schumacher of the Williams team, had expressed a reluctance to travel to the United States for the race.

But the FIA and Formula One chief Ecclestone have insisted the race must go on.

"While we are very saddened by recent events, we continue to plan and work for what we expect will be a successful, exciting event," George said.