Hacking attacks on Chinese computers in 2013 rose by more than half compared with the previous year, with attacks coming from the United States making up a significant proportion, China's top Internet security agency said on Friday.

Beijing and Washington have been squaring off for months over the issue of cyber attacks, each accusing the other of hacking into sensitive government websites.

China has long singled out the United States as the top source of intrusion on its computers.

China's National Computer Network Emergency Response Coordination Center said the country's Internet faced "many security threats," creating a "challenge" for China's overall security.

"There are frequent occurrences of state-level organized Internet hacking attacks, and some of our country's important Internet information systems have been penetrated," it said in a statement on its website.

It said that last year 15,000 host computers were taken control of by Trojan horse malware, and 61,000 websites were taken control of through backdoor breaches from overseas, up 62 percent on the previous year.

Almost 11 million host computers had been taken control of by overseas-based servers, mostly from the United States, South Korea and Hong Kong, with the United States accounting for one-third of the figure, the body said.

Last week, The New York Times and German magazine Der Spiegel said the U.S. government spied on major Chinese telecommunications firm Huawei Technologies Co.

On Thursday, China's Defense Ministry said that it would beef up its Internet security following the report, but also accused the United States of hypocrisy.

The White House has said that the United States does not spy to gain commercial advantage.