The US State Department acknowledged last night it was wrong to report that terrorism declined worldwide last year and admitted that attacks actually increased sharply.

The original finding, that attacks were at a 34-year low, was used to boost one of President Bush's top foreign policy claims - success in his War on Terror.

But Colin Powell, the US Secretary of State, insisted early this morning that the erroneous figures were innocent mistakes.

"We didn't look deeply enough into the data to realise there were inconsistencies in reporting from the way we reported in previous years," General Powell told ABC News.

"We'll put out a corrected report," he said of Patterns of Global Terrorism, released in April.

"There was no attempt to mislead or cook the books in any way," he added.

Richard Boucher, a State Department spokesman, said that statements by senior Bush Administration officials claiming success against terror were based "on the facts as we had them at the time; the facts that we had were wrong."

The erroneous report said that attacks fell last year to 190, the lowest level in 34 years, and had dropped 45 per cent since 2001, Mr Bush's first year as President. Both the number of incidents and victims actually increased sharply, General Powell's department conceded last night.

It said that it was now working to determine the correct figures. Among the mistakes, Mr Boucher said, was that only part of 2003 was taken into account. "The time period was not - apparently they didn't do the full year," he said.

General Powell said that the errors were partly the result of new data collection procedures. "I can assure you it had nothing to do with putting out anything but the most honest, accurate information we can," he said.

"Errors crept in that frankly we did not catch here," he said of the report, which showed a drop in the number of attacks worldwide in 2003 and excluded incidents in which no one died.

Congressman Henry Waxman, a California Democrat, said this week that the Bush Administration had refused to address his contention that the findings were manipulated for political purposes.

Mr Waxman had written to General Powell asking for an explanation. Mr Boucher said that a reply to Mr Waxman was being prepared.

One of Mr Bush's major foreign policy claims has been that his post-September 11 strategy to counter terrorism was showing success.