Chinese cyber spies were accused yesterday of hacking into Pentagon computers to steal details of America's new Joint Strike Fighter, the most expensive fighter jet in history.

Lockheed Martin is developing the jet, at a cost of $300bn (€232bn) and eight countries, including Britain, will buy them.

Hackers were reported to have downloaded "several terabytes of data related to design and electronics systems".

The leak could make it easier for enemies to defend against the plane, also known as the F35 Lightning II.

However, the spies could not access the most sensitive material, which is kept on computers that are not connected to the internet.

Former officials in America told 'The Wall Street Journal' that the attacks appeared to have originated in China, but there is scant concrete evidence because it is easy to mask identities online.

Chinese officials reacted angrily to the accusation.

A spokesman for the foreign ministry said: "China has not changed its stance on hacking. China has always been against hacking and we have cracked down very hard on hacking. This is not a Chinese phenomenon. It happens everywhere in the world."

Attacks on the Pentagon are common, but are said to have escalated dramatically in the past six months, and coincide with growing speculation about China's role in cyber espionage.

China is due to unveil its new generation of submarines tomorrow.

However, officials insisted that they pose no threat to the region.

(Independent)