MEXICO CITY (AFP) - WikiLeaks founder Julian Assange urged US intelligence whistleblower Edward Snowden on Thursday to watch his "physical security" if he travels abroad after Russia gave him a residence permit.

Snowden, a former US intelligence operative who is wanted by the United States on espionage charges, was granted three-year residency by Moscow, allowing him to travel abroad, his lawyer said.

"Of course our advice is that he be extremely cautious in doing so for his physical security," Assange, a Snowden supporter, said in a videoconference held at a freedom of speech forum in Mexico City.

Appearing with a beard and long white hair, Assange has been holed up in Ecuador's embassy in London for more than two years as he fights a Swedish arrest warrant over sexual assault allegations.

The 43-year-old Australian fears that if he goes to Sweden he will be sent to the United States to face charges for publishing classified material.