WASHINGTON, March 19: The United States issued a worldwide caution on Friday, reminding Americans that Al Qaeda planned to use both conventional and non-conventional weapons against them.

The US government also did not rule out the possibility that "Al Qaeda will attempt a catastrophic attack within the United States".

"The US citizens are cautioned to maintain a high level of vigilance, to remain alert and to take appropriate steps to increase their security awareness," the caution said.