China is developing weapons that would disable its enemies' space technology such as satellites in a conflict, the Pentagon said in a report released yesterday.
The annual report to the US Congress on Chinese military power also said that "numerous" intrusions into computer networks around the world, including some owned by the US government, in the past year seem to have originated in China.
Looking at the prospect of more conventional warfare, the report said the situation in the Taiwan Strait was stable but the balance of forces continued to shift in China's favour as Taiwan had reduced defence spending in recent years.
Beijing usually criticises the Pentagon report, saying it unfairly portrays China as a military threat when it is committed to a "peaceful rise" as its economic power grows.
David Sedney, a top Pentagon China specialist, said there was no call for US alarm over China but repeated a frequent US complaint that Beijing has not made clear the reasons for its rapid military modernisation and spending growth.
"I think the biggest thing for people to be concerned about really is the fact that we don't have that kind of strategic understanding of the Chinese intentions," said Mr Sedney, deputy assistant secretary of defence for East Asia.
"That leads to uncertainty," he said, briefing journalists at the Pentagon on the latest report.
Mr Sedney said recent US-China defence talks had been "surprisingly successful", yielding agreements to establish a defence hotline and a dialogue on nuclear strategy and to hold talks on each country's reports on the other's military power.
But he said China's activities in both space and cyberspace were areas of concern.
The report said: "China is developing a multi-dimensional programme to limit or prevent the use of space-based assets by its potential adversaries during times of crisis or conflict."
The report said the Chinese People's Liberation Army had developed weapons and jammers to prevent an enemy using space-based systems such as satellites.
"The PLA is also exploring satellite jammers, kinetic energy weapons, high-powered lasers, high-powered microwave weapons, particle beam weapons, and electromagnetic pulse weapons for counter space application," it said.
US officials have also repeatedly expressed concern about China's shoot down of one of its defunct weather satellites in a test in January last year.
"We continue to ask the Chinese to sit down and talk to us about that test and they haven't," Mr Sedney said.
The US blew apart a defunct satellite of its own with a missile from a Navy ship last month. The Pentagon said that was done purely to prevent potential harm to people.
Under the heading Cyberwarfare Capabilities, the report stated that intrusions apparently from China into computer networks used "many of the skills and capabilities that would also be required for computer network attack".