Swedish prosecutors said on Thursday they had dropped a sexual assault probe against Julian Assange because the time limit on the case had expired.

Some of the allegations against the WikiLeaks founder -- who has been holed up at Ecuador's London embassy since 2012 to avoid extradition -- have reached their statute of limitations after five years.

"Now that the statue of limitations has expired on certain offences, I am obliged to drop part of the investigation," prosecutor Marianne Ny said, adding she still wanted to question the Australian on a more serious rape claim.