British Prime Minister Theresa May (centre) during her visit on Thursday to Salisbury, the town in southern England where ex-spy Sergei Skripal and his daughter are believed to have been attacked with a nerve agent on March 4.
Putin's spokesman denounced the claim as "shocking and inexcusable".
Putin, a former KGB spy who is poised to win a fourth term in an election on Sunday, has so far only said publicly that Britain should get to the bottom of what has happened.
Tusk, who will host the summit as head of the European Council, said on Twitter he had phoned May on Friday "to prepare (a) clear message of the EU on #SalisburyAttack".
The Russians are accused of using a nerve agent against former spy Sergei Skripal and his daughter Yulia. He was later granted British citizenship.
But to the West, they are raising similar concerns.
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SportsLine.com simulated every NCAA Tournament game 10,000 times, and came up with at least one big upset: No. 14 seed Stephen A. Calipari wouldn't want to admit that, because he knows the Blue presence in Nashville would be an added advantage for his team.
Foreign ministry spokeswoman Maria Zakharova said May's statements were "completely insane accusations", and accused Britain of failing to work with Moscow through the OPCW.
The Russian foreign ministry said staff from the UK's Moscow embassy would be expelled within a week.
He said Russian Federation continued to press for samples of the nerve agent identified by British scientists to be handed over to Moscow.
Tanaiste and Foreign Aff-airs Minister Simon Coveney has condemned the attack in Salisbury.
Russian Federation also says it suspects foul play in Glushkov's death and opened its own inquiry Friday.
The rapid endorsement by its European and North American allies of Britain's assessment and retaliatory actions in relation to the Salisbury nerve agent attack is to be welcomed.
The country has demanded access to the case and opened its own investigation into the attempted murders on Friday.
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I'm not about that because I'm not happy all the time, I'm not smiling all the time, by the way". Arias also knows the tie will be very hard .
The four nations called upon Moscow to provide full and complete disclosure of its Novichok nerve agent program to the Organization for the Prohibition of Chemical Weapons.
Moscow has denied allegations of Russian involvement. May's problem is the same one that faces the U.S.in sanctioning Russian Federation: there isn't much left to target.
Speaking to the AP, he called it unlikely that some of the nerve agent could have gone missing in the years after the 1991 collapse of the Soviet Union.
Britain's foreign minister increased pressure on Russian Federation over the poisoning case of one of Moscow's ex-spies by claiming it was "overwhelmingly likely" President Vladimir Putin directly ordered the attack.
Vil Mirzayanov, a Soviet-era chemist who helped create Novichok but later revealed the existence of Moscow's classified programme, said terrorists could not produce it.
Russian Federation says it has destroyed all its chemical weapons and shut down its military chemical programme in the mid-1980s.
"The United Kingdom briefed thoroughly its allies that it was highly likely that Russian Federation was responsible for the attack", the statement reads.
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Wales captain Jones was unimpressed with the remarks made by the Australian, who also called the Irish "scummy". There are changes to all three sections of the forwards while Richard Wigglesworth starts at scrumhalf.
Mr Bristow, after leaving the meeting, said that the United Kingdom had no quarrel with the Russian people and would "always do what is necessary to defend ourselves".
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