GENEVA (Reuters) - Top U.N. human rights experts said on Monday that Russia was to blame for attempting to kill Kremlin critic Alexei Navalny, and called for an international investigation into his poisoning with a “signature compound” last year. The attempt to kill Navalny was part of a pattern of attacks on critics at home and abroad, and intended to send a “sinister warning” to quash dissent, Agnes Callamard, U.N. special rapporteur on summary killings, and Irene Khan, U.N. expert on freedom of opinion and expression, said in a statement. “It is our conclusion that Russia is responsible for the attempted arbitrary killing of Mr. Navalny,” Callamard told a news conference, announcing the findings. “As in other cases, Mr. Navalny was poisoned by a signature compound, this time Novichok, one unlikely to be used by a non-state actor or another government,” she said. Navalny fell ill in Siberia last August and was flown to Germany, which says it found evidence he had been poisoned with Novichok, a banned nerve agent. Russia denies any role in his illness and says it has not seen proof he was poisoned. In a statement, Foreign Ministry spokeswoman Maria Zakharova said Russia hoped the U.N. experts’ intervention would prompt Germany to release data which Moscow has accused Berlin of withholding. “We share the interest in finding out the truth of this incident,” Zakharova said in a statement to Reuters. Callamard, asked about the comment, said: “Russia has more than enough at the moment to carry out its own investigation; it is not up to Germany to provide information.” After recuperating for five months in Germany, Navalny, 44, returned to Russia in January. He was arrested on arrival and sentenced to 2-1/2 years in prison for parole violations. “Given the inadequate response of the domestic authorities, the use of prohibited chemical weapons, and the apparent pattern of attempted targeted killings, we believe that an international investigation should be carried out as a matter of urgency in order to establish the facts and clarify all the circumstances concerning Mr. Navalny’s poisoning,” the U.N. experts said. “The use of Novichok violates Russia’s commitments under the Chemical Weapons Convention. It was meant to kill Mr. Navalny and as such constitutes a violation of the prohibition against arbitrary killings,” they said.