Prime Minister Theresa May said on Wednesday that two Russian spies carried out an attack of neurotoxic agents against a former colleague in British territory, while prosecutors issued an arrest warrant against the suspects.
Prosecutors filed charges against Alexander Petrov and Ruslan Boshirov for attempting to kill former Russian double agent Sergei Skripal and his daughter Yulia with Novichok in the city of Salisbury on March 4.
May told parliamentarians that the two "are officers of the Russian military intelligence service, also known as GRU," adding that the attack was sanctioned from above.
"This was not a dishonest operation, it was almost certainly also approved outside the GRU in a higher level of the Russian state," May said.
The dispute sparked a wave of diplomatic expulsions on both sides, as well as new US sanctions against Moscow, which again denied their participation on Tuesday.
"Unfounded accusations are being made against Russia (…) and absurd demands are being made for explanations in relation to a situation in which we have nothing to do," the Russian Foreign Ministry said in a statement.
"Instead of carrying out an independent, objective and transparent investigation into the incidents in Salisbury and Amesbury, London continues to participate in Russian anti-megaphone diplomacy, continuing its propaganda program," the statement added.
Earlier, a spokeswoman for the Russian Foreign Ministry said the names and photos of the two men wanted by Britain "do not tell us anything" accused London of "manipulating information."
The United States ambassador in London, Woody Johnson, tweeted: "The United States and the United Kingdom stand firm in holding Russia accountable for their act of aggression on the territory of the United Kingdom."
Britain called for an urgent meeting of the United Nations Security Council, expected on Thursday, to update members on the situation.
The Australian prime minister, Scott Morrison, says that Australia is in a closed step with the United Kingdom to make Russia respond by the attack of the nervous agent.
"Australia shares the anger and outrage of the UK at this dangerous and deliberate act by Russia, which also puts the British public, police and other first responders at risk," Morrison said in a statement on Thursday.
European arrest warrant
The Foreign Ministry summoned the Russian Charge d'Affaires in London to demand that Petrov and Boshirov go to Britain for trial, a spokeswoman said.
But prosecutors said they would not formally seek extradition, as Russia made clear in previous cases that it did not extradite its citizens.
In 2007, Russia refused to extradite Andrei Lugovoi, the main suspect in the murder by radioactive poisoning of former Russian agent Alexander Litvinenko in London.
"However, we obtained a European arrest warrant (EAW)," said Sue Hemming of the Crown Prosecution Service.
"(This) means that if a man travels to a country where an EAW is valid, he will be arrested and extradited for these charges," which will never expire.
Britain's top anti-terrorist police officer, Neil Basu, said the two suspects probably traveled to Britain using aliases. The photos of the couple were made public in the hope that someone would recognize them.
He said the couple, who is over 40, flew to London two days before the attack and stayed in a hotel, where Novichok's traces were found in his room.
They visited Salisbury the previous day to conduct a reconnaissance and were captured in security cameras near the house of Skripal.
Police believe they put Novichok, a military-grade nerve agent developed by the Soviet Union during the Cold War, on the door handle.
Skripal and her daughter found themselves unconscious park bench a few hours later. The suspects flew back to Moscow later that night.
Petrov and Boshirov face charges of conspiracy to murder Skripal and the attempted murder of him, his daughter and Nick Bailey, an injured police officer later, prosecutors said.
They are also accused of using banned chemical weapons and causing serious bodily harm to Yulia Skripal and Bailey.
Skripal was a colonel in the GRU who was imprisoned for betraying other agents in the British security service MI6. He moved to England in 2010 as part of an exchange of spies.
The Skripals and Bailey recovered from their poisoning, but on June 30, a British couple fell ill with the same type of nerve agent in the nearby town of Amesbury.
One of them, the mother of three children, Dawn Sturgess, 44, died on July 8.
His partner Charlie Rowley had found and given him a bottle of perfume, falsely labeled "Premier Jour" by Nina Ricci, which police said contained a "significant amount of Novichok".
Rowley was also hospitalized and although he was discharged, he recently returned and is being treated for meningitis and vision loss.
Basu said the British couple was not attacked but fell ill "as a result of the imprudence in which such a toxic nerve agent was eliminated."