Friends of the secretive founder of WikiLeaks, the website behind the biggest leak of United States military documents in history, claimed yesterday that he was the victim of a smear campaign after prosecutors withdrew a warrant for his arrest in connection with rape and molestation allegations.

On Saturday a spokeswoman for the Swedish prosecutors office in Stockholm confirmed that an arrest warrant for Julian Assange had been issued and urged him to "contact police so that he can be confronted with the suspicions".

According to Expressen, the Swedish newspaper, the 39-year-old Australian had been wanted in connection with two separate incidents. The first involved a woman from Stockholm who said he had molested her. The second involved a woman from Enkoping, a town about an hour's drive west of Stockholm, who had accused Assange of rape. The warrant was later withdrawn.

Assange, who has no known addressand spends much of his time travellingto ensure a low profile, had earlier deniedthe charges on WikiLeaks' Twitter page, saying they "are without basis and theirissue at this moment is deeply disturbing".

Assange's online supporters were quick to point the finger at US intelligence agencies. Typical tweets included: "America will silence you one way or another." Another asked: "Can't you spooks frame up with something more original?"

Gavin MacFadyen, director of the Centre for Investigative Journalism, and a friend of Assange, said: "A lot of us who had any notion of what he was doing expected this sort of thing to happen at least a week ago. I'm amazed it has taken them this long to get it together. This is how smears work.

"The charges are made and then withdrawn and the damage is done."

WikiLeaks has courted controversy since July when it posted 77,000 Afghanistan war documents online, leading to claims it had put the lives of troops and security sources at risk. Assange had been in Sweden to oversee the release of thousands more classified documents relating to US military operations. Last week he said that his website was set to publish a final batch of 15,000 documents on the war in Afghanistan in "a couple of weeks".

"It seems an unusual time to embark on a career of multiple rape," said Guardian journalist David Leigh, who has worked closely with Assange over the recent WikiLeaks Afghan documents. "He certainly didn't come across as a violent man, not in the least.

"Julian was clearly preparing to release more sensitive documents, which is what he was doing in Sweden, and he had also been working with Swedish television on a project. What effect this may have on that remains to be seen."

There is speculation that WikiLeaks has a secret code that would decrypt a massive "insurance file" on its site whose contents are the subject of frenzied speculation. The file dwarfs the size of all the other files on the WikiLeaks Afghanistan page combined, prompting claims that it contains a huge amount of top secret material. But sceptics believe the file may simply be an elaborate bluff and that it contains nothing revelatory.

Last week Assange further stoked the flames of controversy when he claimed that the Pentagon was ready to talk to WikiLeaks about its unreleased documents. A Pentagon spokesman said a phone call had been arranged with the WikiLeaks lawyer but no conversation had taken place. He denied that the Pentagon was willing to co-operate with WikiLeaks.

US media reported that federal prosecutors were looking at possible criminal charges against WikiLeaks for releasing the confidential military documents. The Wall Street Journal claimed that the US Defence and the Justice Departments were exploring legal options for prosecuting Assange and others on grounds that they encouraged the theft of US Government property.