Lev Ponomaryov, 67, leader of the organization For Human Rights and a founding member of the Kremlin-rankling organisation Memorial, said he had just stepped out of his car when a stranger asked him for a cigarette and, when he said he does not smoke, someone else struck him on the head from behind.

He said he was knocked to the ground and kicked and beaten by two or three men for about 10 minutes until a doorman came to his aid. He was released from l Thurhospitasday with contusions and bruises to his upper body.

The assailants said nothing during the assault and made no attempt to rob him, Ponomaryov said after being released from a hospital Wednesday. "It was an ordered attack," he told Russia Today. "It’s connected with my human rights activities. I’ve been involved in a few sensitive issues lately."

A Soviet-era dissident who was elected to parliament in the early 1990s, Ponomaryov has worked to expose abuses in the Russian prison system, and he helped establish the Solidarity democratic opposition movement last year.

In recent weeks, he has been outspoken in his criticism of the government’s prosecution of Mikhail Khodorkovsky, the jailed oil tycoon and Kremlin foe facing new charges in a second trial that opened Tuesday in Moscow. Ponomaryov said he had met with Sabine Leutheusser-Schnarrenberger, a rapporteur for the Parliamentary Assembly of the Council of Europe’s human rights committee about the case. She has issues a statement demanding a full investigation into Ponomayov’s attack.

US President Barack Obama, in talks with Russia President Dmitry Medvedev in London, broached the issues of human rights in Russia, specifically the attack on Ponomaryov, White House officials said.

The co-director of For Human Rights, Yevgeny Ikhlov, told the gazeta.ru news site that Ponomaryov had complained to police in recent months that he was being followed, but police had refused to investigate.

“The climate for human rights defenders has been worsening in the past several years,” said Tatyana Lokshina, a researcher for Human Rights Watch in Moscow. “People are just watching their back all the time and thinking, ‘when is it going to happen to me?’ ”

Rarely do the police identify the perpetrators of such attacks, and rights groups have accused the Russian authorities of tacit complicity, if not actual involvement in violence and threats.

Many see a concerted campaign of intimidation that is the result of years of government efforts to portray independent groups as traitors to Russia.

While police, speaking with Russian daily Kommersant, have chalked up the attack to “hooligans,” Vice Chairman of the State Duma Security Committee Gennady Gudkov called the attack a “cynical escapade.”

"The attack on Lev Ponomaryov is a cynical escapade and an instance of street lynching,” Guvkov told Interfax."

“The inability to conduct political discussions leads to the use of ‘might is right’ as a centuries-old method of settling arguments. Unfortunately, the struggle for justice in Russia often ends by violence,” he said.

"This is a tragic trait of the times."

Amnesty International called on Russian President Dmitry Medvedev, who was meeting with President Obama in London, to speak out "against the increasing climate of intolerance towards human rights defenders" in Russia.

"Far too many abuses against human rights and civil society activists, lawyers and journalists have gone unpunished, and perpetrators believe they can act with total impunity," Nicola Duckworth, the organization’s Europe and Central Asia director, said in a statement.

"The continuing silence in view of the many recent threats and attacks will be equivalent to condoning such crimes."

Police offered a different version, saying Ponomaryov had been the victim of ordinary muggers.

“Apparently he fell victim to ordinary street hooligans, who are plentiful in the region, “ a police spokesman told Kommersant. “They asked for a smoke. He refused. One could get a punch in the face for a lesser thing in (the ) Ivanovsk (District of Moscow).”

Ponomaryov himself contested this accounting on gazeta.ru, saying, “If they were just robbers they would be screaming something like ‘give us the money, But those brutes didn’t take my wallet with plenty of money or my laptop.”

In January, a colleague of Ponomaryov’s, human rights lawyer Stanislav Markelov, was gunned down moments after stepping out of a news conference in Moscow, where he had spoken out against the early release from prison of a Russian army colonel who had murdered an 18-year-old Chechen woman.

Anistasiya Baburova, a freelance reporter with the fiercely independent Novaya Gazata – which has lost four reporters over eight years under mysterious circumstances – was killed at Markelov’s side.

Medvedev met on January 29th with Dmirity Muratov, editor of Novaya Gazata – where Markelov also contributed commentary – to convey his condolences. But the motivations behind this and other overtures Medvedev has made toward opposition media and the human rights sector remains unclear.

In February, 72-year-old opposition newspaper editor Yury Grachev was beaten in the Moscow suburb of Solnechonogorsk by unknown assailants. Police investigating the case dismissed the attack on the editor of the investigative newspaper that exposed numerous acts of official corruption, as self-inflicted injuries.

In December, at least one unidentified assailant shot in the head and wounded Shafig Amrakhov, 51, editor of the Murmansk-based online regional news agency RIA. He died after a week in the hospital. Earlier the same month, two unidentified assailants attacked and beat Zhanna Akbasheva, a local correspondent for the independent news agency Regnum, in the North Caucasus republic  of Karachai-Cherkessiya.

On November 13th, Mikhail Beketov, editor of the authority-rankling Khimskaya Pravda, was beaten nearly to death in the Moscow suburb of Khimki. His paper wrote exposés on corruption and campaigned on environmental issues.

Beketov’s supporters say he made enemies by campaigning against a plan to build a toll highway between Moscow and St Petersburg through a forest on the outskirts of Khimki.

None of the cases has been solved.