WASHINGTON (AFP) - Journalists based in the United States got a shock Thursday when they dialled a toll-free number to join a conference call with senior officials accompanying US President Barack Obama in London.

The number turned out to be a sex chat line inviting callers to use their credit card numbers.

"Do you have any hidden desires?" a sultry voiced woman asked.

"Well, do you feel like getting nasty? Then you came to the right place -- brought to you by the girls of Swank magazine," she said.

Reporters finally got through to the two officials in London -- National Security Advisor James Jones and Secretary of State Hillary Clinton -- when they gave up on the US "800" number and instead dialled an international number.

The White House did not offer an explanation when asked how it sent the wrong number in an email listing both numbers -- one for journalists in the United States and the other for those overseas.

"Lots of important issues to cover today!" Thomas Vietor, a White House spokesman, told AFP when asked about the mistake in a follow-up email.

When pressed further about the number, Vietor replied: "I haven't dialled whatever number you're referencing. Please call such numbers on your free time!"

Jones and Clinton were being interviewed about the NATO summit on Friday in Strasbourg, but the contents of the call cannot be released until 0400 GMT (12pm local time), in line with rules stipulated by the White House.