British media had reported that Assange was in Britain after WikiLeaks released a trove of cables exposing the inner workings of American diplomacy.

Assange's legal team has said it will mount a challenge in the British courts to any Swedish attempt to have him arrested and sent to Sweden.

Don't miss

Stephens was not immediately available for further comment.

Once London received a copy of the warrant it deemed legally satisfactory, a police move to arrest Assange was likely to occur quickly, an official source familiar with legal discussions between authorities in the two countries said.

The Swedish prosecution authority at first opened, then dropped and then re-opened the investigation of allegations by two Swedish women. Assange's Swedish lawyer has said his client believed foreign powers were influencing Sweden.

The latest release listed details of sites around the world which the United States considers vital to its interests, including drug companies and energy installations.

Swiss postfinance, the banking arm of state-owned Swiss Post, has closed an account used for WikiLeaks donations because Assange has no residency in Switzerland, a spokesman for the bank said. The online payment service PayPal has also suspended WikiLeaks' account.

US Attorney General Eric Holder said on Monday the Obama administration was considering using laws in addition to the US Espionage Act to possibly prosecute the release of government information by WikiLeaks.

Assange has said he and colleagues are taking steps to protect themselves after death threats.