LONDON - Downing Street has mounted a damage-limitation exercise after the head of the government's top science lab said the precise source of the nerve agent used to poison former Russian agent Sergei Skripal has not been identified.

The Times newspaper in London reported Wednesday that an interview on Sky News with Gary Aitkenhead, CEO of the Defense Science and Technology Laboratory (Dstl), risks undermining Prime Minister Theresa May's international coalition against Moscow.

Under the headline "May battles to preserve alliance against Russia", the Times cites an ally of Germany's Chancellor Angela Merkel raising doubts over Britain's global push to isolate Moscow after Dstl defense laboratory at Porton Down could not confirm that the Salisbury nerve agent came from Russia.

Britain's national media also reported Wednesday that Russia's President Vladimir Putin also seized on the admission by Aitkenhead that he had not identified the "precise source" of the poison, and used it against Skripal and his daughter Yulia.

The Times reported that the interview, approved in advance by Number 10, had caused dismay in Downing Street.

Aitkenhead said his laboratories had identified the nerve agent used to poison the pair as a military-grade novichok, which could probably be deployed only by a nation state.

Putin said that given the lack of precise information about the agent's origin "the speed at which the anti-Russian campaign has been launched causes "bewilderment".

May has yet to comment on the latest development, with the government instead referring to a statement issued by the Foreign Office.

The statement of the Foreign Office says "We have been clear from the very beginning that our world leading experts at Porton Down identified the substance used in Salisbury as a novichok, a military grade nerve agent. This is only one part of the intelligence picture."

But it insisted its assessment that Russia was responsible for the attack, saying "there is no other plausible explanation."

Dstl, in a series of posts on its social media site said: "Our experts have precisely identified the nerve agent as a novichok. It is not, and has never been, our responsibility to confirm the source of the agent."

"This chemical identity of the nerve agent is one of four factors used by the Government to attribute the use of chemical weapons in Salisbury to Russia."

Skripal remain in a serious condition in hospital, while his daughter is recovering in hospital.