Google said some of the hacked accounts belonged to senior US government officials, Chinese political activists, officials in South Korea, military personnel and journalists

China has angrily denied suggestions it was behind an audacious cyber-assault on hundreds of personal Gmail accounts, after Google traced the origin of the attack to a school linked to previous hacking allegations.

The latest accusations are sure to ratchet up tensions between Beijing, which repeatedly insists it opposes hacking, and Washington, which is trying to pressure Beijing and other governments to do more to stop cyber-attacks. "Blaming these misdeeds on China is unacceptable," said a Chinese foreign ministry spokesman Hong Lei. "Hacking is an international problem and China is also a victim. The claims that China supports this kind of hacking are without any basis in fact."

Google's security team engineering director, Eric Grosse, said in a blog posting that the most recent hacking targeted "the personal Gmail accounts of hundreds of users including, among others, senior US government officials, Chinese political activists, officials in several Asian countries (predominantly South Korea), military personnel and journalists".

It is the second time in 17 months that Google has identified China as the site of efforts to hack into its network, and the internet giant said the attack originated in Jinan, the capital of Shandong province and home to the Lanxiang Vocational School, one of two educational facilities linked to a number of cyber attacks last year. Lanxiang bills itself as a school training hairdressers and chefs. It does boast in television adverts that it has the biggest computer laboratory in the world, but maintains that its computer studies courses stick mainly to Microsoft Office.

A New York Times report last year named Lanxiang and one other school in the area as being the source of attacks on Google and dozens of other US corporations. Quoting anonymous sources, it said Lanxiang was established with military support and trained computer scientists for the military – claims denied by the school.

Last year, Google threatened to pull out of China completely over complaints of censorship and hacking assaults. The search engine is now based in Hong Kong, which isn't subject to Beijing's censorship rules. The White House has said no key security breach of official government email accounts took place, but the FBI and Homeland Security in the US are investigating and Hillary Clinton, the US Secretary of State, said the allegations were "very serious".

The Pentagon has this week been on the offensive against cyber-crime, warning on Wednesday that deliberate cyber-attacks on vital computer networks in the US could be considered acts of war.