A State Department official said the warning, whose wording was nearly identical to one issued by the department on March 23, was being released to remind people the threat level remained elevated but did not reflect major new information.

"The Department of State remains concerned by indications that al Qaeda continues to prepare to strike US interests abroad," the department said in language identical to its last "worldwide caution" issued five weeks ago.

"Al Qaeda and its associated organisations have most recently struck in the Middle East and in Europe but other geographic locations could also be venues for attacks," it added, again tracking the previous announcement.

The latest statement was issued nearly five months before the previous warning had been to expire on Sept 23.

"There is a lot of troubling activity. The threat level remains elevated. We are concerned about the continuing and ongoing possibility for actions against American targets," said the State Department official who asked not to be identified.

"Given that general environment, we thought it was appropriate to do this at this time," he added.

The official also noted the main change in the new version was to remove references in the last warning to Israel's killing of Hamas leader Sheikh Ahmed Yassin and the possibility that might spark attacks on Americans.

"The idea was to make it as timeless as possible so that we don't have to keep putting these out every time (something happens)," he said.

The department also issued a new version of its warning to US citizens about the danger of "terrorist" attacks in the Middle East and North Africa that closely followed the previous one on March 23 but also dropped references to Yassin's killing.