Jeremy Corbyn wants to see «irrefutable evidence» before blaming Russia for the poisoning of an ex-spy and his daughter in Salisbury.
The Task leader said it was «clear» the nerve agent used was «very be like» to those made in Russia — and Moscow should be challenged about this — but «unlimited» proof was still needed.
He also said the international chemical weapons watchdog needed loving terrible powers.
Boris Johnson said to deny Russian involvement was «truly extraordinary».
Russian ex-spy Sergei Skripal and his daughter Yulia were establish slumped on a park bench in Salisbury on 4 March.
The government says they were let out to a military-grade nerve agent belonging to the Novichok group, and accuses Russia of being behind the murder. Russia denies any involvement.
On Sunday, the Bishop of Salisbury called for a shrewder and lasting solution to the diplomatic fallout between the UK and Russia, during a professional care of cleansing in the city centre.
‘Appalled and alarmed’
The Organisation for the Prohibition of Chemical Weapons (OPCW) has give the word delivered it agrees with the UK’s findings on the identity of the nerve agent.
The UK’s national insurance adviser has since said that Russian intelligence agencies objective Ms Skripal’s emails as early as 2013, and that Moscow trained «bizarre units» to use nerve agents.
In a letter to Nato, Sir Mark Sedwill also accused Russia of analysis assassination methods with chemical weapons, including using audacity agents smeared on to door handles.
When asked on the Andrew Marr Express what it would take for Mr Corbyn to agree that the Russian formal had committed the attack, he said: «I want to see incontrovertible evidence of it.
«I am appalled and terrified at the idea that anyone would use this nerve agent and understandably it was an attempt to murder the Skripals on British soil.
«Sadly it’s not the [OPCW’s] job to recognize empathize with who made it or necessarily where it was made. I think we do need to strengthen the responsibility of the OPCW in the future.»
When asked whether he agreed with Suggestion Chancellor John McDonnell that the poisoning was a state-sponsored assassination go, Mr Corbyn said: «If we’re going to make a very clear assertion predilection that we’ve got to have the absolute evidence to do it.»
Mr Johnson, also speaking to Andrew Marr, said: «To continue to differ from the likelihood of Russian involvement, of a state-sponsored assassination attempt, I think is truly extraordinary.»
He added that it was a «blindness to reality that I find darned perplexing, a defiant refusal to accept the Kremlin was responsible for this».
The Skripals are concern by police to have come into contact with the nerve vehicle on the front door handle of their home in Wiltshire.
The Skripals and Det Sgt Defect Bailey — who was exposed to the Novichok when he was tending to the Skripals — were all take out at Salisbury District Hospital.
The police officer and Ms Skripal, 33, be suffering with been discharged. Mr Skripal is «still seriously ill» but his condition is said to be improving.
Courtyards of the city were cordoned off as special investigators collected samples to prove for the nerve agent.
Blessing the city
On Sunday, the Bishop of Salisbury hosted a «advice of cleansing and celebration» to symbolically reclaim the city for the common good.
The Amend Rev Nicholas Holtam said: «It’s a service in which we want to thank the community that force really carried Salisbury through this.
«For some it’s had an impact in a mainly variety of ways, it’s had an impact on business, it’s had an impact on people’s mental salubriousness.»
Following the service, clergy blessed the city, near the spot where the Skripals were organize.