Assange had lived inside the Ecuadorian embassy from June 2012 to April 11 this year, when Ecuador lifted his asylum and allowed British police to enter the embassy and arrest him.
A US law enforcement source told Reuters that Manning will likely be jailed again if she refuses to comply with a new grand jury subpoena.
Assange is also fighting a legal battle against extradition to the United States, where he is wanted for his part in the release of a trove of classified military and diplomatic cables. Swedish authorities have had to shelf it because Assange was living at the embassy at the time and there was no prospect of bringing him to Sweden. Assange had been hiding in the Ecuadorian embassy there since 2012 while escaping extradition to Sweden for the sexual assault investigations.
The Wikileaks founder, currently in Belmarsh prison in London, now faces likely extradition from Britain.
An arrest warrant for Assange was issued on November 18, 2010 by Ny on suspicion of rape, three counts of sexual molestation and one count of unlawful coercion. "It is also my intention in the near future [to ask] that the district court order Mr Assange remanded in absentia", said Persson, speaking in Stockholm.
The Swedish lawyer for Assange, Per E. Samuelson, said he was "very surprised" by the decision to reopen the investigation.
Assange has always insisted that allegations of rape are false and offered in the past to travel to Sweden for questioning on condition that the government could guarantee he would not be extradited to the US.
WikiLeaks editor-in-chief Kristinn Hraffnson said Monday that Sweden's "investigation has been dropped before and its reopening will give Julian a chance to clear his name".
The alleged victim, who says she met Assange at a WikiLeaks conference in Stockholm, filed a complaint in August 2010. He is now being held at Belmarsh prison in London.
Shortly after that, Assange entered Ecuador's embassy, and remained there for nearly seven years.
Persson told a press conference in Stockholm on Monday that it would be up to British authorities to determine which extradition request-to Sweden or to the USA - would take precedence.
A British judge has given the US government a deadline of June 12 to outline its case against Assange. "That is not something I can forget", he said.
His eviction from the embassy on 11 April came after a souring of relations, with Ecuador's president Lenin Moreno claiming the Australian had tried to use the Knightsbridge site for spying.
"I do not understand the Swedish prosecutor's. reasoning for reopening a 10-year old case", he said. One wrote that "it was the police who made up the charges" and told a friend that she felt that she had been "railroaded by police and others around her".