The websites were hit by so-called distributed denials of service (DDoS), which direct a firehose of traffic towards targeted servers in a bid to knock them offline, the ministry said.
"Currently, there is no knowledge of other impacts than the lack of access to web portals - there are thus no operational consequences for the defence," it said on Twitter.
(Reporting by Jacob Gronholt-Pedersen and Stine Jacobsen)
