THE Kremlin says Britain will have to apologise for unfounded accusations against Russia over the poisoning of an ex-spy.

Speaking in Ankara, Russian President Vladimir Putin cited the head of Britain’s defence laboratory who said that its scientists couldn’t identify the precise source of the nerve agent used to attack former double agent Sergei Skripal and his daughter.

Mr Putin’s spokesman Dmitry Peskov told reporters that Britain will have to apologise to Russia for its “mad accusations” that “have no foundation whatsoever.”

Mr Peskov says that London will have to account for its claims before its allies, who have evicted scores of Russian diplomats in a show of solidarity.

Britain blames Russia for the March 4 attack on Skripal and his daughter, a claim that Moscow denies.

It came as the head of the UK’s Porton Down military research facility said his scientists have not verified that the nerve agent which poisoned Skripal and his daughter Yulia in the English city of Salisbury, came from Russia.

Gary Aitkenhead, chief executive of the Government’s Defence Science and Technology Laboratory, said the poison had been identified as a military-grade Novichok nerve agent which could probably be deployed only by a nation-state.

Mr Aitkenhead also told Sky News he flatly denied Russian claims the substance could have come from Porton Down itself.

The identification of Novichok was a key plank in the evidence presented by UK prime minister Theresa May’s ability to recruit international support in the dispute with Moscow, resulting in the expulsion of more than 100 Russian diplomats from over 20 countries.

Asked about his scientists’ findings, Mr Aitkenhead said: “We were able to identify it as Novichok, to identify it was a military-grade nerve agent.

“We have not verified the precise source, but we have provided the scientific information to the Government, who have then used a number of other sources to piece together the conclusions that they have come to.”

Mr Aitkenhead’s comments come a day before a meeting of the global chemical weapons watchdog in The Hague to discuss the Salisbury attack. The meeting on Wednesday has been called by Russia to “address the situation around allegations of noncompliance” with the chemical weapons convention made by the UK against Moscow.

The British Foreign Office dismissed the meeting as a “diversionary tactic” by Russia.

But Russian President Vladimir Putin called for a thorough investigation into the poisoning during a visit to Turkey on Tuesday.

Putin said, given the lack of precise information about the agent’s origin, “the speed at which the anti-Russian campaign has been launched causes bewilderment”.

Russia has denied responsibility for the March 4 attack, with foreign minister Sergey Lavrov even suggesting on Monday it might have been carried out by the UK as a means of distracting voters from its difficulties with Brexit. Earlier on Tuesday, deputy foreign minister Alexander Grushko said in comments relayed by Russian news agencies, that the Skripals’ poisoning was a “provocation arranged by Britain” in order to justify high military spending because “they need a major enemy.”

But rejecting Russian claims the substance could have come from Porton Down, Mr Aitkenhead said: “There’s no way that anything like that would ever have come from us or leave the four walls of our facilities.”