WASHINGTON, Nov 11: World leaders have been flooding US President George Bush with congratulatory calls since his re-election victory, but at least one - Spain's Jose Luis Rodriguez Zapatero - appears to be having trouble getting through.

Socialist Prime Minister Zapatero, who angered Bush by pulling Spain's troops out of Iraq earlier this year, "has tried to reach out" to the U.S. president since last week's election, White House spokesman Scott McClellan told reporters on Wednesday.

But Bush has yet to return the call. "Calls are scheduled at times that are mutually convenient. Some calls are able to be scheduled quicker than others," McClellan explained.

A senior Bush administration official denied any snub over the Spanish withdrawal, which Bush warned had emboldened the terrorists.

The official said Bush had received "numerous congratulatory calls from world leaders (and) is in the process of returning those calls."

Other world leaders have also tried to reach Bush since the election but have yet to get through.

Bush was a close ally of Spain's conservative prime minister, Jose Maria Aznar, before Zapatero swept to power.

While Bush has yet to take Zapatero's call, the White House said he had a "private meeting" with Aznar at the White House on Tuesday.

Bush has already spoken to French President Jacques Chirac and German Chancellor Gerhard Schroeder.-Reuters