Intelligence officials in the US have warned police agencies that al-Qaeda may be planning attacks using fuel tankers in major US cities.
Officials say fuel trucks could be driven into petrol stations
The warning said fuel-laden vehicles could be hijacked and rammed into petrol stations to explode.
The cities of New York, Chicago and Los Angeles are reported to be major targets.
However, FBI officials have stressed that the information which led to the warning has not been substantiated.
The possible attacks are reported to be being planned to coincide with the fourth anniversary of the 11 September 2001 attacks.
"Attacks are planned specifically for New York, Chicago and Los Angeles," said the memo, issued on Wednesday to police authorities in Los Angeles.
It added that it was "unclear whether the attacks will occur simultaneously or over a period of time."
The memo adds that those planning to hijack the vehicles would probably be part of small al-Qaeda cells already present in the country.