WikiLeaks' chief spokesman Julian Assange was arrested on Tuesday by U.K. police after turning himself in to authorities, the Metropolitan Police said in a statement.
Assange, 39, of Australia, has been accused of one count of unlawful coercion, two counts of sexual molestation and one count of rape stemming from incidents with two women in Sweden in August.
He was arrested by the Metropolitan Police's Extradition Unit at 9:30 a.m, GMT and is due to appear later on Tuesday in City of Westminster Magistrates Court. A magistrate will likely set bail for Assange, according to a police spokesman.
Assange has maintained that his encounters with the women were consensual, and Swedish prosecutors initially dropped rape charges.
However, Swedish Director of Public Prosecution Marianne Ny re-opened the investigation into the rape charges and said she wanted to question Assange, who was allowed to leave Sweden after the incidents.
Since then, Assange has spent time in the U.K., making few public appearances. The pressure has intensified on him as WikiLeaks began releasing portions of 250,000 secret U.S. diplomatic cables late last month.
Some U.S. politicians have called for his arrest, while the U.S. Attorney General's office is investigating whether he could be charged under the Espionage Act for releasing the material.
The U.S. Army has already charged Private First Class Bradley E. Manning with mishandling and transferring classified information in connection with the cables and a video of an Apache helicopter shooting civilians in Iraq. He is believed to have passed the material to WikiLeaks.
Meanwhile, WikiLeaks has taken steps to make its infrastructure more resilient after its Web site came under repeated denial-of-service attacks. WikiLeaks was also booted from Amazon Web Services after it was briefly hosted on its servers.
But more than 350 other Web sites are now up that are distributing WikiLeaks' content, posing further difficulties for authorities seeking to halt the release of the material.