Boris Johnson has accused Russia of trying to conceal “the needle of truth in a haystack of lies” over the Salisbury spy poisoning.
Arriving for a meeting with EU counterparts in Brussels, the Foreign Secretary said Moscow’s denials over the incident were “increasingly absurd” as he accused the Kremlin of changing its story regarding the Novichok nerve agent Britain says was used in the attack.
Mr Johnson said: “Today the technical experts from the Organisation for the Prohibition of Chemical Weapons are arriving in the UK to take the samples from Salisbury, and meantime the Russian denials grow increasingly absurd.
“At one time they say that they never made Novichok, and at another time they say they did make Novichok, but all the stocks have been destroyed … but some of them have mysteriously escaped to Sweden, or the Czech Republic, or Slovakia, or the United States, or even … the United Kingdom.
“I think what people can see is that this is a classic Russian strategy of trying to conceal the needle of truth in a haystack of lies and obfuscation.”
In a joint statement, the Foreign Affairs Council said: “The European Union takes extremely seriously the UK Government’s assessment that it is highly likely that the Russian Federation is responsible.
“The European Union is shocked at the offensive use of any military-grade nerve agent, of a type developed by Russia, for the first time on European soil in over 70 years.
“The use of chemical weapons by anyone under any circumstances is completely unacceptable and constitutes a security threat to us all.
“The Union calls on Russia to address urgently the questions raised by the UK and the international community and to provide immediate, full and complete disclosure of its Novichok programme to the OPCW.
“The European Union expresses its unqualified solidarity with the UK and its support, including for the UK’s efforts to bring those responsible for this crime to justice.”
The move came as Russia’s Tass news agency reported the Kremlin is insisting the UK either backs up its “unfounded allegations” regarding Moscow’s involvement in the Salisbury attack, or apologises.
Tass quoted Kremlin spokesman Dmitry Peskov saying: “Sooner or later they will have to be responsible for these allegations: they will either have to provide some evidence or apologise.”
This followed Vladimir Putin’s dismissal of claims of Russia being behind the Salisbury spy poisoning as “nonsense” as he was re-elected president.
Sergei Skripal and his daughter Yulia would have died instantly if they had been attacked with a nerve agent, the leader said as he celebrated the start of another six-year term.
“The first thing that comes to my mind is that should it really be a warfare agent, people would have died instantly,” he said.
“It is an obvious fact. Russia does not possess such agents. We have destroyed all our chemical arsenals under control of international observers.”
He added: “We are ready for co-operation and said that immediately. We are ready to take part in all necessary probes but the will of the other side is needed for that. So far, we see none.”
Moscow mocked the UK, claiming the Government’s response had fuelled an increase in support for Mr Putin in the election.
The national security council will meet in the coming days to discuss Moscow’s tit-for-tat response to the UK’s expulsion of 23 Russian diplomats.
Mr Johnson is also holding talks with Nato secretary general Jens Stoltenberg on Monday.
Mr Skripal, a former double agent, and his daughter may have been exposed to a deadly nerve agent through his car’s ventilation system, US media has reported.
The pair are still fighting for their lives after being exposed to Novichok two weeks ago in the Wiltshire city.
Downing Street said the OPCW team would meet the UK’s Defence, Science and Technology Laboratory at Porton Down before taking samples of the poison for testing in laboratories overseas.
The Prime Minister’s official spokesman said the testing process could be expected to take “no less than two weeks”.
The spokesman told reporters: “The OPCW inspectors are here. They will be meeting with officials from the Defence, Science and Technology Laboratory and police to discuss the process of collecting samples.
“These will then be dispatched to highly reputable international laboratories which are selected by the OPCW for testing.”