Urgent warnings have been circulated throughout Nato and the European Union for secret intelligence material to be protected from a recent surge in cyberwar attacks originating in China.

The attacks have also hit government and military institutions in the United States, where analysts said that the West had no effective response and that EU systems were especially vulnerable because most cyber security efforts were left to member states.

Nato diplomatic sources told The Times: “Everyone has been made aware that the Chinese have become very active with cyber-attacks and we’re now getting regular warnings from the office for internal security.” The sources said that the number of attacks had increased significantly over the past 12 months, with China among the most active players.

In the US, an official report released on Friday said the number of attacks on Congress and other government agencies had risen exponentially in the past year to an estimated 1.6 billion every month.

The Chinese cyber-penetration of key offices in both Nato and the EU has led to restrictions in the normal flow of intelligence because there are concerns that secret intelligence reports might be vulnerable.

Sources at the Office for Cyber Security at the Cabinet Office in London, set up last year, said there were two forms of attack: those focusing on disrupting computer systems and others involving “fishing trips” for sensitive information. A special team has been set up at GCHQ, the government communications headquarters in Gloucestershire, to counter the growing cyber-threat affecting intelligence material. The team becomes operational this month.

British and American cyber defences are among the most sophisticated in the world, but “the EU is less competent”, James Lewis, of the Centre for Strategic and International Studies, said. “The porousness of the European institutions makes them a good target for penetration. They are of interest to the Chinese on issues from arms sales and nuclear non-proliferation to Tibet and energy.”

The lack of routine intelligencesharing between the US and the EU also contributes to the vulnerability of European systems, another analyst said. “Because of Britain’s intelligence-sharing relationship with America our systems have to be up to their standards in a way that some of the European systems don’t,” he explained.

Jonathan Evans, Director-General of MI5, warned in 2007 that several states were actively involved in large-scale cyber-attacks. Although he did not specify which states were involved, security officials have indicated that China now poses the gravest threat. Beijing has denied making such attacks.

Robert Mueller, FBI Director, has warned that, in addition to the danger of foreign states making cyber-attacks, al-Qaeda could in the future pose a similar threat. In a speech to a security conference last week, Mr Mueller said terrorist groups had used the internet to recruit members and to plan attacks, but added: “Terrorists have shown a clear interest in pursuing hacking skills and they will either train their own recruits or hire outsiders with an eye towards combining physical attacks with cyber-attacks.”

He said that a cyber-attack could have the same impact as a “well-placed bomb”. Mr Mueller also accused “nation-state hackers” of seeking out US technology, intelligence, intellectual property and even military weapons and strategies.To help to fight the growing threat, the Office of Cyber Security, set up last year as part of the Government’s national security strategy, liaises with America’s so-called cyber czar, Howard Schmidt, who was appointed by President Obama to protect sensitive government computers.

British officials said that everyone in sensitive jobs had been warned to be especially cautious about disseminating intelligence and other classified information. Whether British intelligence is involved in retaliatory attacks is never confirmed. However, officials said that there was a significant difference between being part of an information war and indulging in aggressive attacks to disrupt another country’s computer systems.

Dr Lewis said that neither the US nor any of its Western allies had formed an effective response to the Chinese threat, which has its origins in a massive boost to Chinese technology ordered by Deng Xiaoping, the late Chinese leader, in 1986. The West’s own cyber offensives have so far been directed largely at terrorists rather than nation states, giving China virtually free rein to penetrate Western systems with its own world-class hackers and increasingly popular Chinese-made components. “You almost have to admire them,” Dr Lewis said. “They have been very consistent in their goals.”