The crowd also stood without waving flags as Formula One racing paid respect to the victims of terrorist attacks in the United States.

After the one minute of silence there was spontaneous but restrained applause from the crowd.

In a sign of mourning, world champion team Ferrari started some cars with a black nose during practice.

Italian organizers, citing the auto racing's highest ruling body, said the remaining season races of the season will be held -- at Indianapolis on Sept. 30 and in Japan on Oct. 14.

However, some drivers voiced concern about racing in the United States so soon after the attacks in New York and Washington.

"I'm worried, because we are going to race in a country which is in a state of emergency," French driver Jean Alesi said. "To race at Indianapolis is not an easy decision to take."

Jarno Trulli, the Italian driver of the Jordan team, said: "If we actually travel to Indianapolis, it will not be in a normal, tranquil situation."

"There are some fears on the drivers' side ... it will be a difficult trip for everybody," he said.

Ralf Schumacher, the younger brother of world champion Michael, said he wouldn't take his family to Indianapolis if he goes.

"There's a big danger for the drivers and fans since no one knows what will happen. An event that has 100,000 spectators and without special security precautions, as is the case here, could be a target for attacks," said Schumacher, who drives with the Williams-BMW team.

His teammate, Colombian rookie Pablo Montoya, had a different approach.

"I have a contract and I'm going to drive where Williams decides to compete," he said.