UK officials will face their Russian counterparts later as they brief the UN Security Council on two men suspected of the Salisbury nerve agent attack.
Prosecutors say there is evidence to charge the pair, who the PM said are thought to be officers from Russia’s military intelligence service the GRU.
Ex-Russian spy Sergei Skripal, 66, and his daughter Yulia, 33, were poisoned with Novichok on 4 March.
Moscow denies any involvement in the attack.
Theresa May told the Commons on Wednesday the suspects entered the UK on Russian passports using the names Alexander Petrov and Ruslan Boshirov.
She said the poisoning was “not a rogue operation” and was “almost certainly” approved at a senior level of the Russian state.
Det Sgt Nick Bailey also fell ill after responding to the incident in Salisbury.
Police are also linking the attack to a separate Novichok poisoning on 30 June, which led to the death of Dawn Sturgess.
Britain called Thursday’s meeting of the UN Security Council a day after Theresa May addressed MPs about the suspects.
Russia is a permanent member of the Security Council and will be represented at the meeting alongside UK allies the US and France.
BBC security correspondent Gordon Corera said the aim of the meeting is to maintain pressure on Russia.
But our correspondent said it is also thought there will be less visible activity, including covert work by British intelligence to try to disrupt the activities of the GRU.
Mrs May has also said Britain will push for the EU to agree new sanctions against Russia.
Ahead of the UN meeting, Australia said it was “in lock step with the UK on the importance of holding Russia to account” over the “dangerous and deliberate act”.
The CPS is not applying to Russia for the extradition of the two men, as Russia does not extradite its own nationals.
But a European Arrest Warrant has been obtained in case the pair travel to the EU.
Responding to the naming of the suspects, Russia’s London embassy called on the British government to “give up politicised public accusations”.
The embassy accused the UK authorities of being unwilling to engage with them, by providing additional information about the suspects such as their passport numbers.
Russian President Vladimir Putin’s foreign policy adviser Yuri Ushakov told reporters the names of the Russian suspects “do not mean anything to me”.
What is the GRU?
Analysis by BBC security correspondent Frank Gardner
Less famous than the KGB – or its successor, the FSB – the GRU plays a shadowy but important role in Moscow’s strategic plans.
It is Russia’s military intelligence arm, reporting directly to the defence minister. It has extensive cyber and signals operations and has been accused of hacking and online sabotage.
GRU officers are often stationed in embassies around the world and many were expelled after the Salisbury attack in March.
Since 2013 Russia’s elite Spetznaz (Special Purpose) Special Forces have been part of the GRU’s command structure and are believed to have played a part in the annexation of Crimea in 2014. British government officials maintain that the GRU’s operations include assassinations both inside Russia and overseas.
Sergei Skripal served in the GRU as a military intelligence officer in Afghanistan in the 1980s. In 2006 he was arrested and jailed after reportedly betraying the names of his GRU colleagues to Britain’s MI6. In 2010 he was allowed to leave for Britain as part of a prisoner swap, but in the Kremlin’s eyes he will always be seen as a traitor.
The Metropolitan Police said the two men arrived at Gatwick Airport from Moscow on 2 March and stayed at the City Stay Hotel in Bow Road, east London.
On 4 March they travelled to Salisbury – having also visited for reconnaissance the previous day – where Mr Skripal’s front door was contaminated with Novichok.
Officers believe a modified perfume bottle was used to spray the door.
The pair flew from Heathrow to Moscow later that night.
While traces of Novichok were found in the London hotel room, there is no risk to other guests who were staying at the hotel at the time, police said.
They now want to hear from anyone who was a guest there from 4 March to 4 May.
Police said Ms Sturgess and her partner Charlie Rowley were later exposed to Novichok in Amesbury, near Salisbury, after handling a contaminated container, labelled as Nina Ricci Premier Jour perfume.
Mr Rowley told police he found the box containing the small bottle and an applicator – all found to be counterfeit – in a charity bin.
He tried to put the two parts together and got some of the contents on himself. His partner Ms Sturgess applied some of the contents to her wrists and became unwell.
The bottle, with a modified nozzle, had contained a “significant amount” of Novichok, Scotland Yard said.
The Crown Prosecution Service says Petrov and Boshirov should be charged with offences including conspiracy to murder; attempted murder and the use and possession of Novichok contrary to the Chemical Weapons Act.
The offences only relate to the Salisbury attack. Police said officers are continuing to work with the Crown Prosecution Service on the Amesbury incident.