The Dutch security service AIVD is investigating the possibility that Chinese tech company Huawei is involved in spying for the Chinese authorities by leaving a ‘back door’ open to information about customers at one of the three big telecom combines, the Volkskrant said on Thursday.

The paper bases its claims on security service sources but the AIVD has refused to comment.

Vodafone/Ziggo and KPN also declined to comment on the report while T-Mobile/Tele2 said it is ‘not aware’ of any operation involving the AIVD. Huawei told the paper that it does not cooperate with espionage.

‘In every country in which we operate, we obey the law and we protect our clients’ privacy,’ a spokesman told the paper.

The Volkskrant did not give more details about what form the ‘back door’ is said to take and whether it is a bug or has been deliberately placed.

Dutch telecoms giant KPN said last month it intends to select a ‘western’ company to work on the critical core of its 5G rollout after a wave of criticism from MPs and the US ambassador to the Netherlands about the potential involvement of Huawei.

And the AIVD in April warned about the risks of using Chinese equipment for crucial infrastructure and said digital attacks and espionage by countries such as China, Iran and Russia pose a real threat.