"Belgium assesses these malicious cyber activities to have been undertaken by Chinese" hacker groups, a Belgian foreign ministry statement dated Monday read.

It said their activities had targeted the defence and interior ministries and "significantly affected our sovereignty, democracy, security and society at large."

"Belgium strongly denounces these malicious cyber activities, which are undertaken in contradiction with the norms of responsible state behaviour as endorsed by all UN member states," it said.

"We continue to urge the Chinese authorities to adhere to these norms," Brussels added, demanding Beijing "take all appropriate measures" to investigate.

In December last year, a cyber-attack on the Belgian defence ministry paralysed its web-connected IT systems for several days -- although Belgian security services insist no sensible data were accessed.

It remains unclear who authored that attack which highlighted a security loophole in the Java-based Apache Log4j logging utility where a hacker, allegedly sponsored by the Chinese state, was able remotely to introduce spyware.

mad/jug/cpy/cdw/ah

CHINA CONSTRUCTION BANK