The paper said that British police knew where the internet whistle-blower was -- believed to be a location in southeast England -- but could not act on the information as the European arrest warrant was incorrectly filled out.
Swedish authorities issued the warrant -- in connection with alleged sex offences -- on November 19, a day before Interpol placed him on their wanted list.
However, a police source told the paper the warrant was unenforceable.
"It is not a properly certified warrant so we can't act on it," the source said.
Assange's British-based lawyer Mark Stephens said the authorities knew his whereabouts.
"The police know how to get hold of him, as does the Swedish prosecutor. Yet no one seems concerned to tell us what is going on," he said.
Assange has not been seen since his WikiLeaks website began the release over 250,000 official US documents on Sunday.