The US has underlined its determination to hold those responsible for the criminal leak of secret American documents by whistleblower website Wikileaks, saying for now the arrest of Julian Assange "is an issue between Britain and Sweden."

"Well, our investigation is ongoing. And beyond that, as to his arrest, this is, at this point, an issue between Britain and Sweden,  the State Department spokesman, P J Crowley, told reporters.

39-year-old Assange, an Australian citizen, was arrested by the UK Metropolitan police in London yesterday on the basis of an arrest warrant issued from Sweden relating to allegations of sexual assaults against him.

Assange was also produced before Westminster Magistrates Court where he was denied a bail.

"What we re investigating is a crime under U.S. law.

The provision of 250,000 classified documents from someone inside the government to someone outside the government is a crime," he said at his daily news conference.

"And as we ve said, we will hold those responsible fully accountable. That investigation is still ongoing,  Crowley underlined.

Crowley said the US position has been clear from the outset that the release of these documents puts lives and interests at risk, not just American lives and American interests, but the interests of others around the world.

"We have specifically called on Mr. Assange to return stolen property to the United States. He has declined to do that. But beyond that, without talking about any particular cable, there is information that fully deserves confidentiality and classification,  he said.

He said the release of a list of critical infrastructure that is important to our society and our economy and the economies of other countries is "irresponsible".

"It is expressly the kind of information that is classified and deserves to remain classified. And its release, in essence, is providing a targeting list to a group like al-Qaeda," Crowley said.

Responding to questions, Crowley said he does not expect any major reshuffle of US diplomats in the foreign countries in view of the Wikileaks.

"I don t expect that to happen," he said.

He said it was "complete nonsense" that there s some vast global conspiracy centered on the United States.

He said US diplomats are doing "what we expect them to do and what we need them to continue to do". "None of that will change based on these revelations," he underlined.

"To the extent our relations with other countries are based on mutual interest and mutual respect, that hasn t changed by the release of these documents," Crowley said.