Washington has launched a war of words over cybersecurity against China before President Xi Jinping's US trip next month, a move that analysts say attempts to set the agenda for the state visit and put pressure on Beijing.

During a CBS Evening News television interview on Tuesday, US Secretary of State John Kerry accused China and Russia of "very likely" reading his e-mails.

Cyberattacks have been a topic of ongoing discussions with China and will be so again when US President Barack Obama hosts Xi in Washington in September, the top US diplomat said.

Kerry's allegation followed an NBC report that claimed Chinese "cyberspies" have accessed the private e-mails of "many" top Obama administration officials since at least April 2010.

Zhu Haiquan, spokesman for the Chinese embassy in Washington, dismissed the NBC report.

He told Chinese media on Monday that China is a major victim of cyberattacks, and that the Chinese government firmly opposes all forms of cyberspying.

Fighting cross-border cyberattacks requires international cooperation, while "groundless accusations and microphone diplomacy won't resolve any problems but only make things worse", Zhu said.

Li Haidong, a professor of US studies at China Foreign Affairs University, said Washington is trying to inflame the issue through a series of accusations against China as a means of setting the agenda for Xi's upcoming visit to the US.

"Washington often stands against China over issues like cybersecurity and the South China Sea, as it believes that China's diplomacy and growing economic clout challenge US global leadership," Li said.

Ni Feng, an expert on US studies at the Chinese Academy of Social Sciences, said that US cybertechnologies are far more advanced than China's, and that the US business sector is a main force behind the US government's pressing China.

Financial Times reported in July that the FBI has labeled China "the most dominant threat" to US companies and believes Beijing was the main culprit behind a sharp increase in economic espionage cases its agents were investigating.

Ni said the two sides haven't found a solution to issues such as cybersecurity, and previous dialogues over the topic stalled after the US indicted five Chinese military officers last year on allegations of cybertheft.

But he added that Xi's visit is expected to go smoothly and hardly be affected by the accusations - a measure that the US often uses to take the initiative before a high-level visit.