The Norwegian parliament said at the time it had been targeted in a global cyberattack on Microsoft Exchange Servers blamed on Chinese state-backed groups.
The parliament had been hit by another hack seven months earlier blamed on
a Russia-based group.
“We summoned the embassy of China earlier in the day,” Foreign Minister Ine Eriksen Søreide told a news conference.
“We clearly told them that this sort of attack is unacceptable.”
She added that the attack was carried out “from China” but stopped short of directly blaming the Chinese state.
The United States, the European Union and Britain have blamed China for the March cyberattack.
In a statement, China’s Oslo embassy said it was “waiting for the Norwegian side to provide evidences for today’s claim”.
“Cyber security requires cooperation and collective effort other than political manipulation,” it added.
In 2010, China reacted angrily after the Nobel peace prize was given to jailed Chinese dissident Liu Xiaobo.
The incident affected ties between Oslo and Beijing even though the award is made by an independent panel.