UN, July 21 (RIA Novosti) - UN rights experts have offered Russia help in conducting an investigation into the murder of Memorial activist Natalya Estemirova, the UN press service said on Tuesday.

Estemirova, who had been investigating kidnappings and disappearances in Chechnya for the human rights group, was abducted and murdered last Wednesday in the south Russian republic, resulting in international outrage.

The move by seven leading international experts comes after a call by UN High Commissioner for Human Rights Navi Pillay for a thorough and independent probe into the killing.

The experts said they had taken note of Russia's condemnation of the murder and its pledge to do all it could to catch and punish Estemirova's killers.

"However, these assurances will be worth little unless the authorities take steps that go beyond what has been done in the past which has all too often led to a cycle of impunity," they said in a statement.

"We offer our assistance to the Russian authorities in light of the failure to effectively and impartially investigate the killings and attacks on a number of human rights defenders in recent years...and to bring the perpetrators to justice."

Russian President Dmitry Medvedev dismissed as "primitive" a theory implicating Chechen President Ramzan Kadyrov in the murder, but Oleg Orlov, the head of Memorial, accused Kadyrov of involvement.

In a statement published on Memorial's website last Wednesday, Orlov said: "I know, I am certain who is to blame for the murder of Natasha Estemirova. We all know this person. His name is Ramzan Kadyrov, the president of the Chechen Republic."

Kadyrov retaliated by initiating legal action against Orlov on libel and defamation charges.