Chinese hackers spied on the computers of five European foreign ministries over the summer, according to research from US security company FireEye.
The hackers sent emails with malware-ridden attachments purporting to detail a possible US intervention in Syria.
The company has not revealed which ministries were targeted but said the malware samples were meant for individuals involved in the G20 talks.
In total nine computers had been compromised, the company told the BBC.
The computers had been targeted in the run-up to the annual summit of the G20 group of nations - which includes China - in St Petersburg, Russia, in September, FireEye said. The talks were dominated by the civil war in Syria.
For a week in August, the researchers said, they had been able to monitor one of the 23 computer servers used by the hackers, which they have dubbed the Ke3chang group after the names of one of the files used in its malicious code.
During the week the malware had been observed in action, no documents had been stolen, they said.
"At that stage it appeared to be about network reconnaissance," senior FireEye researcher Narottama Villeneuve told the BBC.
The Ke3chang group has been active since at least 2010, according to the researchers.
Traditionally it has targeted the aerospace, energy and manufacturing industries but they have also delivered malware to hi-tech companies and governments, according to FireEye.
In 2012 it used a London Olympics themed attack and a year earlier used emails purporting to show nude pictures of the then French president's wife, Carla Bruni, researchers said.
But in their latest attack "they appeared to be specifically targeting foreign ministries", Mr Villeneuve told the BBC.
"The hackers were based in China but it is difficult to determine from a technology point of view how or if it is connected to a nation state," he added.
Mr Villeneuve explained how he had gained entry to the hackers' server.
"When they shift infrastructure, the servers are open. I just happened to check the servers when they weren't secured," he said.
However the glimpse into the inner workings of the hackers' command and control centre was short-lived, lasting for just over a week.
Tensions between China and the West over cyber-espionage have been increasing in recent years.
In June the US Defence Secretary Chuck Hagel accused Chinese hackers of accessing secret US weapons programmes.