A member of Jeremy Corbyn's frontbench team has backed the Government over its mass expulsion of Russian diplomats, saying it would have been "easier for us" if the Labour leader made it clear he supported the move too.
Mr Corbyn received fierce criticism from Conservatives and some of his own MPs after his team raised doubts about who was responsible for the Salisbury nerve agent attack.
A group of Labour backbenchers said it "unequivocally accepts" the Russian state's culpability for the incident, while Theresa May said it was "outrageous" that Mr Corbyn's spokesman had said there was a "problematic" history over the use of UK intelligence.
Shadow defence secretary Nia Griffith said that it was "quite clear" that, due to the nature of the chemical weapon used, it had been an "act of aggression".
"And that is why we are fully supporting the expulsion of 23 diplomats," she told the Daily Mirror.
Ms Griffith said senior Labour figures had been briefed by security services over the attack on Sunday March 4 that left Sergei Skripal and his daughter Yulia fighting for their lives.
Asked if Mr Corbyn had undermined UK security assessments that it was "highly likely" Russia was behind their poisoning, Ms Griffith said: "Looking back, perhaps it would have been easier for us if he had made it clear at the beginning of what he said, just how much we support the expulsion of the diplomats.
"It would have been easier and perhaps we would not have had the conversations we are seeing."
Ms Griffith's comments were quickly supported by several Labour MPs.
Exeter MP Ben Bradshaw said she was "spot on", while Kingston Upon Hull North MP Diana Johnson said she "fully" supported the shadow defence secretary.
The Sun, meanwhile, reported that shadow foreign secretary Emily Thornberry told a London seminar: "We utterly condemn this despicable act and support all the measures taken by the Government today."
Mr Corbyn's spokesman's comments prompted Labour backbencher John Woodcock to table an Early Day Motion "unequivocally" accepting the "Russian state's culpability" for the attack, and supporting "fully" the statement made by Mrs May in the Commons.
The motion was swiftly signed by a number of prominent critics of Mr Corbyn, some of whom went public with their criticism of the leader's senior aide Seumas Milne.
Labour MP Anna Turley tweeted: "I'm afraid Seumas doesn't speak for my Labour or British values", while Chuka Umunna said: "Mr Milne's comments do not represent the views of the majority of our voters, members or MPs."
The Labour spokesman said the Government may have more information.
He told reporters: "The Government has access to information and intelligence on this matter which others don't.
"However, also there is a history in relation to weapons of mass destruction and intelligence which is problematic, to put it mildly.
"So, I think the right approach is to seek the evidence to follow international treaties, particularly in relation to prohibitive chemical weapons."
Asked if he could rule out the possibility of Russia being framed, the spokesman said the evidence pointed "overwhelmingly" to the two options set out by the PM.
"In the meantime I think it is essential we follow the evidence and what the evidence produces," he added.