China has strongly rebutted the groundless claim it conducted a cyberattack targeting Microsoft Exchange email servers as "sheer slander" and urged the United States and its allies to stop "splashing dirty water" on China and dismissed their accusations.

"The accusation against China by the UK side is sheer fabrication and slander," said a spokesperson for the Chinese embassy in the United Kingdom. "The Chinese side is gravely concerned and strongly opposed to this. We call on the UK side to immediately stop echoing the groundless and irresponsible accusation against China."

On Monday, the US led the UK, the European Union, Australia, Canada, New Zealand, Japan and the North Atlantic Treaty Organization in accusing China of using "Chinese State-backed actors" to carry out hacking of Microsoft Exchange email servers earlier this year.

"China is a staunch defender of cybersecurity and a main victim of cyberthefts and attacks," the spokesperson said.

Foreign Ministry spokesman Zhao Lijian said at a regular news briefing in Beijing on Tuesday that China will take necessary measures to firmly defend its cybersecurity and its own interests.

Zhao said that the groundless accusations that the US has mustered its allies to carry out against China on the issue of cybersecurity are fabricated.

"It is purely smear and suppression out of political motives. The Chinese side will never accept it," he said, adding that a small number of countries cannot represent the international community, and smearing others cannot whitewash oneself.

According to a Chinese cybersecurity tech center, about 52,000 overseas command and control servers controlled about 5.31 million hosts on the Chinese mainland last year.

In February this year alone, 830,000 computers with IP addresses in China suffered unknown attacks, 70 percent of which came from abroad, including the US.

Last September, China put forward the Global Initiative on Data Security, which calls for countries to stand against information and communications technology activities that impair or steal important data of crucial infrastructure in other countries.

Zhao said that China's position is clear and consistent: It firmly opposes and combats any form of cyberattacks and will not encourage, support or condone any cyberattacks.

Zhao also said that in fact it is the US that is the largest source of cyberattacks in the world.

He cited a report from a Chinese cybersecurity company that said an organization of the US Central Intelligence Agency had carried out an 11-year-long cyber infiltration and attack targeting China's key sectors, including aerospace, scientific institutions, the oil industry, large internet companies and government institutions.

"Such attacks severely undermined China's national security and economic security, and the key infrastructure security and personal information security of the public," Zhao said.

"If NATO really cares about cybersecurity in its member states, then it should first discuss the matter of extensive cyber espionage of a certain member state on other member states," Zhao added.

China's embassies in Canada and New Zealand also called for the countries to "abandon the Cold War mentality, adopt a professional and responsible attitude when dealing with cyber incidents", and stop "manipulating political issues under the pretext of cybersecurity and mudslinging at others".

The spokesperson for the Chinese Mission to the EU said that NATO has made repeated and groundless accusations against China.

"A certain country in the West has abused its technological advantages for massive and indiscriminate eavesdropping across the world, even on its close allies," the spokesperson added.

China's embassy in Australia said that "the US has engaged in unscrupulous, massive and indiscriminate eavesdropping on many countries including its allies. It is the world champion of malicious cyberattacks".

Earlier this year, media reports said that Denmark's secret service helped the US spy on its close allies, including German Chancellor Angela Merkel, from 2012 to 2014.

Norway claimed on Monday that an earlier cyberattack on its Parliament's email system was carried out by forces from China. China's embassy in Norway said it is reasonable to question and doubt whether this is a "collusively political manipulation "by Western powers against China.

Zhao Ruinan in Beijing contributed to this story.