Moscow has claimed it wants to ascertain as soon as possible the identities of the two men named by Britain as suspects in the nerve agent attack on a former Russian spy in Salisbury, and has asked London to help.

“We need to establish who these people are, if these are [Russian] citizens or not,” said Maria Zakharova, the foreign ministry spokeswoman on Friday. “We want to do this with maximum haste and effectiveness, and so we are again appealing to Britain for help in ascertaining the identities of these people.”

Britain announced charges in absentia on Wednesday against two men believed to be officers with Russia’s military intelligence service, known as the GRU. Theresa May said the men flew into Britain in March to try to murder Sergei Skripal, a former GRU officer who sold secrets to MI6, and accused the Russian government of orchestrating the operation.

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Scotland Yard said the alleged secret agents travelled to Britain under the names of Alexander Petrov and Ruslan Boshirov, which were probably aliases. The Kremlin has described the allegations as unacceptable and denies that any Russian officials were involved.

Zakharova also accused May of a “frank lie” over her claims that Russia had not offered Britain information after the nerve agent attack, and suggested that May had “selective access” to Russian media reports.

Dmitry Peskov, a spokesman for Vladimir Putin, said on Thursday that Russia would not investigate the two suspects because it had not received a formal request for legal assistance from Britain.

Zakharova’s comments came as a purported ex-GRU officer claimed the attempted murder was too amateurish to have been the work of professional secret service agents.

If GRU agents had wanted to target Skripal, they would have done it “quietly, without fuss, and brought him [to Russia] in a mail bag, and no one would have known where he had gone,” Ivan Tarasov told Russia’s Komsomolskaya Pravda newspaper.

Tarasov also claimed the Skripals could have been targeted by a Russian crime gang, possibly over unpaid debts, and mocked reports that the suspects stayed in the same room in a cheap hotel near Salisbury. “That’s how bandits act, not professional secret service officers. GRU officers don’t stay in London hotels,” he said.

The purported ex-GRU officer also suggested that the suspects could have used novichok in a bid to confuse British investigators by pointing the finger of blame at the Kremlin.