美安全局G20峰会监视梅德韦杰夫

Leaked documents reveal Russian president was spied on during visit, as questions are raised over use of US base in Britain.

American spies based in the UK intercepted the top-secret communications of the then Russian president, Dmitry Medvedev, during his visit to Britain for the G20 summit in London, leaked documents reveal.

The details of the intercept were set out in a briefing prepared by the National Security Agency (NSA), America's biggest surveillance and eavesdropping organisation, and shared with high-ranking officials from Britain, Australia, Canada and New Zealand.

The document, leaked by the NSA whistleblower Edward Snowden and seen by the Guardian, shows the agency believed it might have discovered "a change in the way Russian leadership signals have been normally transmitted".

The disclosure underlines the importance of the US spy hub at RAF Menwith Hill in Harrogate, North Yorkshire, where hundreds of NSA analysts are based, working alongside liaison officers from GCHQ.

The document was drafted in August 2009, four months after the visit by Medvedev, who joined other world leaders in London, including the US president, Barack Obama, for the event hosted by the British prime minister, Gordon Brown.

Medvedev arrived in London on Wednesday 1 April and the NSA intercepted communications from his delegation the same day, according to the NSA paper, entitled: "Russian Leadership Communications in support of President Dmitry Medvedev at the G20 summit in London – Intercept at Menwith Hill station."

The document starts with two pictures of Medvedev smiling for the world's media alongside Brown and Obama in bilateral discussions before the main summit.

The report says: "This is an analysis of signal activity in support of President Dmitry Medvedev's visit to London. The report details a change in the way Russian leadership signals have been normally transmitted. The signal activity was found to be emanating from the Russian embassy in London and the communications are believed to be in support of the Russian president."

The NSA interception of the Russian leadership at G20 came hours after Obama and Medvedev had met for the first time. Relations between the two leaders had been smoothed in the runup to the summit with a series of phone calls and letters, with both men wanting to establish a trusting relationship to discuss the ongoing banking crisis and nuclear disarmament.

In the aftermath of their discussions on 1 April, the two men issued a joint communique saying they intended to "move further along the path of reducing and limiting strategic offensive arms in accordance with the treaty on the non-proliferation of nuclear weapons".

A White House official who briefed journalists described the meeting as "a very successful first meeting focused on real issues". The official said it had been important for the men to be open about the issues on which they agreed and disagreed. Obama had stressed the need to be candid, the official noted.

While it has been widely known the two countries spy on each other, it is rare for either to be caught in the act; the latest disclosures will also be deeply embarrassing for the White House as Obama prepares to meet Vladimir Putin, who succeeded Medvedev as president, in the margins of the G8 summit this week.

The two countries have long complained about the extent of each other's espionage activities, and tit-for-tat expulsions of diplomats are common. A year after Obama met Medvedev, the US claimed it had broken a highly sophisticated spy ring that carried out "deep cover" assignments in the US.

Ten alleged Russian spies living in America were arrested.

Putin was withering of the FBI-led operation: "I see that your police have let themselves go and put some people in jail, but I guess that is their job. I hope the positive trend that we have seen develop in our bilateral relations recently will not be harmed by these events." Last month, the Russians arrested an American in Moscow who they alleged was a CIA agent.

The new revelations underline the significance of RAF Menwith Hill and raise questions about its relationship to the British intelligence agencies, and who is responsible for overseeing it. The 560-acre site was leased to the Americans in 1954 and the NSA has had a large presence there since 1966.

It has often been described as the biggest surveillance and interception facility in the world, and has 33 distinct white "radomes" that house satellite dishes. A US base in all but name, it has British intelligence analysts seconded to work alongside NSA colleagues, though it is unclear how the two agencies obtain and share intelligence – and under whose legal authority they are working under.据英国《卫报》6月16日报道，有泄露的文件披露，美国驻英间谍在俄罗斯总统德米特里·梅德韦杰夫2009年赴伦敦出席G20峰会期间监听他的绝密通信。

美国国家安全局是美国最大的监视和窃听机构、美国国家安全局在简报中与英国、澳大利亚、加拿大和新西兰的高官分享了监听细节。

《卫报》所看到的泄密文件由爱华德·斯诺登提供，该文件显示，美国国家安全局认为其可能发现了俄领导层在惯常的信号传达方式上的变化。

文件起草于2009年8月。4个月前，梅德韦杰夫、美国总统巴拉克·奥巴马和其他国家领导人一起在伦敦出席英国首相布朗主持的峰会。

据美国国家安全局的文件，梅德韦杰夫于4月1日抵达伦敦，美国国家安全局当天就截获了其代表团的通信。文件名为：“伦敦G20峰会上俄领导人德米特里·梅德韦杰夫总统的通讯支持——截获于曼威斯山站。”

文件的开头是照片上是梅德韦杰夫笑容满面地分别与布朗和奥巴马会谈的两张照片。

报告称：“这是一份对德米特里·梅德韦杰夫总统伦敦之行的信号活动分析。本报告详述了俄罗斯领导层在信号传输方式上的变化。信号从俄罗斯驻英国大使馆传出。”美国国家安全局截获的俄领导人通讯是在奥巴马和梅德韦杰夫第一次会见几小时之后。

虽然，美俄两国互相监视已是众所周知的事情，然而任何一方被当场抓住的情况还是很罕见；最新的爆料文件让白宫感到十分尴尬，因为奥巴马准备在本周G8峰会期间和普京进行会见。

美俄长期以来互相指责对方间谍活动，且经常针锋相对地驱逐外交官。在奥巴马会见梅德韦杰夫一年之后，美国声称破获了俄间谍网，说该间谍网在美国执行“深度潜伏”任务，并逮捕了10名生活在美国的俄罗斯人。

普京对此表示：“我看到你们警察把一些人投进了监狱，但我想这是他们的本职工作。我希望我们最近趋于改善的双边关系不会因此受到伤害。”而上月，俄罗斯人在莫斯科逮捕了一名美国人，称他是一名美国中央情报局间谍。

这凸显了曼威斯山英国皇家空军基地的美国间谍中心的重要性。该基地位于英格兰北约克郡哈罗盖特，那里驻有数百美国国家安全局分析师，和英国政府通信总部的联络官并肩工作。这块560英亩（约3400亩）的基地在1954年被租给美国，美国国家安全局自1966年起就在那里建有一个大型基地。

这里被视为世界上最大的监视和窃听基地，有33处明显的白色“雷达罩”。虽然尚不清楚这两个机构如何获取和分享情报，已有英国情报分析师在此与美国同行一起工作。