Images circulated by Norwegian dailies VG, Dagbladet, Dagens Naeringsliv and Aftenposten showed investigators carrying cardboard boxes into Jagland's Oslo residence.
The raid by Norway's white-collar crime unit Oekokrim came a day after the Council of Europe, the continent's leading human rights watchdog, which Jagland led from 2009 to 2019, lifted his diplomatic immunity.
"Oekokrim is currently conducting searches of Thorbjoern Jagland's residence and recreational properties. This was expected and is a standard part of an investigation of this nature," Jagland's lawyer Anders Brosveet said in a statement.
Jagland is accused of aggravated corruption, his lawyer added, under Norway's legal code that precedes formal charging and allows a suspect to get a lawyer and the police to arrest a suspect at some point.
In Norway, formal charges are brought against someone much later in the legal process, sometimes only weeks before a court case begins.
"This does not represent any real change in the substance of the case but is a legal consequence of the investigative methods used by the police," Brosveet said.
"I am very glad that the matter is being clarified," Jagland was quoted as saying by Aftenposten on Thursday.
Oekokrim said that in addition to Jagland's Oslo home, it had searched a property in a town on Norway's southern coast and one in the nearby mountainous county of Telemark.
It was planning to question Jagland as well.
"As a consequence of the search, Jagland is now accused of aggravated corruption. Jagland will be questioned by Oekokrim," Oekokrim's chief Paal Loenseth told Reuters.
Jagland is also a former foreign minister and ex-chair of the Nobel Peace Prize committee.
"Jagland wishes to contribute to ensuring that the case is thoroughly clarified, and the next step is that he will appear for questioning by Oekokrim – as he himself has stated he wants," Brosveet said.
"We will adhere to the process and continue to fully co-operate with the authorities."
The decision to investigate was based on information revealed by newly released files related to Epstein, a financier and convicted US sex offender who died in prison in 2019.
The files indicate, among other things, that Jagland and Epstein's assistants made detailed plans in 2014 for Jagland, his wife, two children and his son's girlfriend to visit Epstein in Palm Beach, Florida, and the Caribbean island that he owned.
Jagland has denied ever visiting Epstein's private island.
The former prime minister has not been charged with any crime but the investigation will seek to uncover whether gifts, travel and loans were received in connection with his official position, police have said.
In a 2014 email, Jagland sought Epstein's help in financing an apartment in Oslo.
Emails from 2018 show Epstein asking Jagland to arrange for him to meet Russian Foreign Minister Sergei Lavrov and saying he had insights to offer President Vladimir Putin.
Jagland promised to bring it up with Lavrov's assistant.
The US Justice Department's release of millions of internal documents related to Epstein has exposed his ties to a range of European figures in business, academia, government and royalty.
