We are obligated to strike back with utmost force after such provocation by American hackers

Honkers' Alliance

Chinese activists have targeted US organisations, including a major news agency and the country's railway regulator, the US Surface Transportation Board.

Its computer system was put out of action on Monday.

Experts say some of the attacks could be coming from hackers outside the two countries.

But a member of one of two groups of Chinese activists involved told the BBC that hackers in China were now planning to target a broader range of US sites.

Wang Wei: Death caused a storm

He said the Chinese hackers had initially focused on official US websites, posting patriotic and anti-American slogans, to express their anger at the loss of a Chinese pilot in the recent collision between a Chinese fighter and a US surveillance plane.

Hackers have also posted pictures of the dead pilot, Wang Wei.

But the Beijing-based hacker said Americans had targeted all kinds of Chinese websites and had placed pornographic pictures on the home page of the official Beijing radio station.

He said his group, known as the Honkers' Alliance, aimed to hit 1,000 US websites of various types over the next two days.

Two waves of attack

The onslaught is timed to coincide with China's 4 May public holiday, which commemorates Chinese resistance to foreign powers in the early part of the 20th century.

Hacked US sites

Department of Labor Department of Health and Human Services US House of Representatives US Surgeon General Department of Energy US Interior Department

The hacker said there would also be a series of attacks on 18 May, the second anniversary of the bombing by Nato of the Chinese embassy in Belgrade.

He said members of his group had received no official support and had met through internet chat rooms.

Many are believed to be students who have led the way in criticisms of the US on Chinese internet bulletin boards in recent weeks.

There has been no official condemnation of the hackers, though police have warned Chinese websites to be on the alert for attacks from the US.