China’s government has denied reports that it spied on the servers at the African Union’s Chinese-built headquarters for more than five years, gaining access to confidential information.

In an investigation published by French newspaper Le Monde, China, which also paid and built the computer network at the AU, allegedly inserted a backdoor (in French) that allowed it to transfer data. The hack wasn’t detected until Jan. 2017 when technicians noticed that between midnight and 2 am every night, there was a peak in data usage even though the building was empty. After investigating, it was found that the continental organization’s confidential data was being copied on to servers in Shanghai.

China’s ambassador to the AU dismissed the reports as “absurd” and “preposterous.” Kuang Weilin told reporters in Ethiopia that it was “very difficult to understand” Le Monde’s claims and that the story was certain to “create problems for China-Africa relations.”

The revelations come as African presidents convene in Addis Ababa to attend the continental summit on governance. In 2012, when the AU building was completed, it was signified as a symbolic gesture aimed at solidifying Sino-Africa relations. The landmark 20-story office tower overlooking a pearl-shaped conference center was “a gift” from the Chinese government to help African nations integrate better and improve their institutional capacity.

But the alleged data theft puts a spin on that rosy affair and might strain the relationship between the two sides. China is heavily involved in Africa, with its companies and entrepreneurs conducting trade and investing heavily in African countries. Chinese aid has also been blamed for propping up authoritarian regimes, constructing shoddy roads and infrastructure built by imported Chinese workers, and focusing mainly on countries home to oil, minerals, and other resources that China needs. But China is also cultivating the next generation of African leaders, with Beijing taking thousands of African leaders, bureaucrats, students, and business people to China for training and education.

Since the discovery of the hack, the AU has allegedly acquired its own servers and refused Chinese offers to reconfigure them. Algerian and Ethiopian officials also combed through the building, checking for any suspicious materials and microphones.

Electronic communications are also now encrypted and reportedly no longer pass through the state-owned operator Ethio Telecom. Ethiopia, home to the third largest number of diplomatic missions in the world after New York and Geneva, is also known for its own cyber surveillance and for cracking down on internet freedom. Last month, a report by the Citizen Lab at the University of Toronto’s Munk School of Global Affairs found that the Horn of Africa nation was using Israeli spyware to surveil dissidents and critics based in 20 countries across the world.