China and the United States traded hacking charges on Sunday as Washington accused Beijing of stealing US intellectual property and the Chinese authorities expressed concern over US cyberattacks.

The back-and-forth between the United States and China over cyber spying followed new claims by former National Security Agency contractor Edward Snowden that the US spy agency was snooping on Chinese targets.

Snowden told Hong Kong's Sunday Morning Post that US spies had hacked the prestigious Tsinghua University in Beijing -- home to one of six "network backbones" that route all of mainland China's Internet traffic -- and the Hong Kong headquarters of Pacnet, which operates one of the Asia-Pacific region's largest fiber-optic networks.

Snowden, who arrived in Moscow on Sunday, reportedly on his way to Venezuela, also said the US spy agency was hacking Chinese mobile phone companies to gather data from millions of text messages.

NSA chief Keith Alexander, asked by ABC television if his agency carries out such activities as hacking Chinese cellphones to steal SMS messages, said "we have interest in those who collect on us as an intelligence agency.

"But to say that we're willfully just collecting all sorts of data would give you the impression that we're just trying to canvass the whole world," he said.

"The fact is what we're trying to do is get the information our nation needs, the foreign intelligence," Alexander said. "That's what you'd expect us to do. We do that right."

Asked if the United States was "losing the cyber war to China," Alexander said: "Our nation has been significantly impacted with intellectual property, the theft of intellectual property by China and others.

"That is the most significant transfer of wealth in history."

Earlier Sunday, China said it was "gravely concerned" over cyberattacks by US government agencies.

Foreign ministry spokeswoman Hua Chunying, according to state news agency Xinhua, said the latest reports "again proved that China is the victim of cyberattacks, and we have already lodged representations to the US side."

Xinhua meanwhile called the United States the world's "biggest villain" for IT espionage, after the new allegations emerged.

"These, along with previous allegations, are clearly troubling signs," Xinhua said in a commentary.

"They demonstrate that the United States, which has long been trying to play innocent as a victim of cyberattacks, has turned out to be the biggest villain in our age," it said.

The United States and China are both victims of hacking and have to work together on the issue, Xinhua said.

But it stressed: "The ball is now in Washington's court. The US government had better move to allay the concerns of other countries."

In her comments, Hua said China opposes all forms of cyberattacks.

"We are willing to enhance dialogue and cooperation with the international community in a spirit of mutual respect, to jointly safeguard peace and security in cyberspace," she said.