MOSCOW - There is no clear proof that Russia is linked to an attack involving a nerve agent against a former Russian double agent in England, the Kremlin spokesman said on Friday, commenting on U.S. President Donald Trump's suggestion that there was."It's obvious that there is a lack of any clear proof (of Russian involvement)... The whole wave (of such statements) originated from Britain," the state-run RIA news agency quoted Dmitry Peskov as saying.Former double agent Sergei Skripal and his daughter Yulia remain in critical condition in hospital after being found unconscious on a bench in the English city of Salisbury on March 4. Russia has repeatedly denied any involvement in the attack.Britain, the United States, Germany and France jointly called on Russia on Thursday to explain the attack. Trump, echoing the British government, said it looked as though Moscow was behind the attack.