Days after the leakage of top secret US surveillance programs threatened to dislodge newly founded cooperation between Washington and Beijing on cyber espionage, China demanded an explanation over the claims by former intelligence contractor Edward Snowden.

The Chinese foreign ministry decided to break its silence Monday, rejecting as “nonsense” suspicions on Snowden’s ties with Beijing and demanding an explanation over the surveillance programs.

“We believe the United States should pay attention to the international community’s concerns and demands and give the international community the necessary explanation,” the foreign ministry said in a statement.

Washington has long accused Beijing of sponsoring cyber attacks and the issue has become a flashpoint in the two countries’ relations.

According to Snowden, still based in Hong Kong, the National Security Agency has access to millions of customers’ data from internet and phone companies, and the US had hacked civilian targets in China for years.

Many have expressed support for Snowden in the city and in the mainland. Chinese state media has called on Beijing to protect him, saying that an extradition would be unwise and “not only a betrayal of Snowden’s trust but a disappointment for expectations around the world”.