The TV report showed what it said was a UK diplomatic spy

Lyudmila Alexeyeva, head of the Moscow Helsinki Group, said the government was trying to turn public opinion against NGOs it wanted to shut down.

Russia said spies posing as diplomats funded NGOs and used a hi-tech "letterbox" disguised as a rock.

The UK government denies any improper behaviour towards Russian NGOs.

They are preparing public opinion for a government move to close us down, which they can now do under the new law Lyudmila Alexeyeva head of the Moscow Helsinki Group, Spying finds new forms Russian press on spy case

The allegations emerged in a Russian TV report on Sunday and were later backed up by the internal state security service, the FSB.

Ms Alexeyeva, head of the Moscow Helsinki Group, said they were part of a campaign against Kremlin critics, linked to a law tightening control over NGOs which President Vladimir Putin signed this month.

"They are preparing public opinion for a government move to close us down, which they can now do under the new law," she told reporters.

She said a document written in Russian which showed one of the alleged spies' signatures was a fake. All communication between her organisation and British donors was in English, according to Ms Alexeyeva.

'Red-handed'

The FSB backed the claims made on Russia's Rossiya TV channel which showed what it said were British agents retrieving data from the dummy, loaf-sized rock planted on a street.

The device is said to be a hi-tech version of the classic "dead drop"

According to the programme, a UK diplomat made regular payments to Russian non-governmental organisations.

The programme named four individuals it described as British spies working as diplomats and also mentioned a Russian citizen, said to be now in custody after confessing to espionage.

The four were named in the programme as Christopher Pirt, Marc Doe, Paul Crompton and Andrew Fleming.

"The most important thing is that we caught them red-handed while they were in contact with their agents [and established] that they were financing some non-governmental organisations," said FSB chief spokesman Sergei Ignatchenko.

He did not detail what action would be taken by the Russian authorities, saying only that the question would be "decided at the political level". The new law on NGOs bans foreign funding of any NGO with "political purposes" but it does not spell out what this means.

KEY RUSSIA-UK SPY CASES 1999 - Defector names Melita Norwood as Russia's longest-serving spy in UK 1985 - KGB double agent Oleg Gordievsky defects to UK hidden in a car boot 1971 - UK expels 105 Russian officials suspected of spying 1951 - First two of the five 'Cambridge spies' exposed 1940 - Defector General Walter Krivitsky gives UK first insight into Soviet intelligence system Hidden history - key cases

It also appears that the alleged donations took place before the new law took effect.

The UK Foreign Office says it is well known that the UK government gives financial support to projects implemented by Russian NGOs in the field of human rights and civil society.

"All our assistance is given openly and aims to support the development of a healthy civil society in Russia," a statement said.

Michael Evans, defence editor of the UK Times newspaper, told the BBC that Russia was still regarded as a centre of espionage.

"I've no idea whether it's true, but clearly there is a lot of intelligence gathering that goes on," he said.