London(CNN) The leaders of the United States, France, Germany and Canada have backed Britain's assessment that two suspects accused of poisoning a Russian ex-spy and his daughter in the UK were Russian military intelligence officers, and that the Russian government "almost certainly" approved the attack.
British Prime Minister Theresa May presented the assessment parliament on Wednesday, after prosecutors said they had "sufficient evidence" to charge two Russian nationals in connection with attack.
Sergei Skripal and his daughter, Yulia Skripal, were poisoned with the military-grade nerve agent Novichok in the English city of Salisbury in March, in a case that triggered a diplomatic crisis between the UK and Russia. The Skripals and a police officer who were hospitalized in the attack have all been discharged.
Britain's Crown Prosecution Service said the two suspects traveled to the UK as Alexander Petrov and Ruslan Boshirov, almost certainly aliases. Prosecutors are seeking charges of conspiracy to murder, attempted murder, the use and possession of Novichok, and causing grievous bodily harm.
"We have full confidence in the British assessment that the two suspects were officers from the Russian military intelligence service, also known as the GRU, and that this operation was almost certainly approved at a senior government level," the leaders said in a joint statement on Thursday.
The leaders also urged Russia to fully disclose its Novichok program to the Organization for the Prohibition of Chemical Weapons, an international watchdog.
"We, the leaders of France, Germany, the United States, Canada and the United Kingdom, reiterate our outrage at the use of a chemical nerve agent, known as Novichok, in Salisbury on March 4," the letter said.
The letter also noted the UK's assessment that Novichok also poisoned Dawn Sturgess and Charles Rowley, a couple living in Amesbury, near Salisbury. They became ill after exposure to liquid in a perfume bottle they found in a charity bin. Sturgess died on July 8 as a result of her exposure to Novichok. UK investigators have formally linked the two cases, but police said the couple did not appear to have been deliberately targeted.
Prosecutors have obtained a European Arrest Warrant and the police are seeking to circulate Interpol Red Notices. The Russian constitution does not permit extradition of its own nationals.
While the two Russians are believed to have been traveling under aliases, they had genuine Russian passports, prosecutors said.
Russian Foreign Ministry spokeswoman Maria Zakharova dismissed the claims. "A link with Russia is being alleged. The names published in the media, like the photos, do not tell us anything," she said.
She called on the British authorities "to move from public accusations and information manipulation to practical cooperation through law enforcement agencies" and repeated Russia's demand that they answer Moscow's queries about the case.
"The investigation of such serious crimes -- which the UK side has repeatedly alleged -- requires the most careful work, scrupulous analysis of data and close cooperation," she said.
More than 20 countries have supported the UK in its allegations against Russia, expelling more than 100 Russian diplomats between them. The US also imposed new sanctions on Russia over the case, which the Kremlin criticized as "categorically unacceptable" and "illegal."