"What has happened is a complete failure. It is very serious. It was in breach of the law and exposed Sweden and Swedish citizens to harm," Löfven said at a press conference in Stockholm on Monday.
It emerged last week that Sweden’s security police Säpo investigated Transportstyrelsen after key information was made available to IT workers in other countries who had not gone through the usual security clearance checks when the agency outsourced IT maintenance to IBM in 2015.
IT workers in the Czech Republic were able to access all stored information during the period including confidential police databases containing criminal records and information on people suspected of crimes, according to reports in the Swedish media.
An SVT report that the records also contained a register detailing all of Sweden’s military vehicles was not accurate however, according to Sweden’s Armed Forces.
Löfven held a press conference on the matter on Monday along with Transportstyrelsen's new general director Jonas Bjelfvenstam, Säpo chief Anders Thornberg and Swedish Armed Forces Supreme Commander Micael Bydén.
Bjelfvenstam called the incident "unacceptable" but added that there were no signs any confidential information had been spread beyond those who had access to it.
Opposition politicians have reacted with outrage to the revelations. Center Party leader Annie Lööf called it "damning", adding that there are "major consequences for the individuals affected and for Sweden’s security".
Criticism has been levelled at Infrastructure Minister Anna Johansson and Minister for Home Affairs Anders Ygeman in particular. The latter will be grilled about the scandal at the Riksdag’s parliamentary justice committee on Tuesday.
Johansson meanwhile claimed that her former state secretary Erik Bromander kept her unaware of the situation until January this year, despite having information on the matter as early as February 2016. She even said that Ygeman also had information in early 2016.
“I can say that I was not informed and that is of course bad. But above all this is a disaster at Transportstyrelsen,” Johansson told news agency TT.
Löfven said he was unaware of the incident until January this year. He said he would in retrospect have liked to be informed about it at an earlier stage, but did not appoint blame to any of his ministerial colleagues for not doing so. He said it was Johansson's, not Ygeman's, job as infrastructure minister to inform him of Transportstyrelsen business, and that she had not been able to as she had not had that information.