New Zealand has welcomed the progress the United Kingdom has made in identifying those accused of deploying a nerve agent in the UK.
Two Russian men charged over the Salisbury poisonings are officers of Russian President Vladimir Putin's military spy agency, Theresa May has told the House of Commons.
"Prime Minister May has indicated that the UK authorities have undertaken a careful and systematic inquiry," said Deputy Prime Minister Winston Peters.
The UK said that after a thorough criminal inquiry the independent Crown Prosecution Service has enough evidence to bring charges against two Russian nationals.
"We said from the outset of Prime Minister May announcing this investigation that we should wait for it to be completed to draw our conclusions, and we have. This is the way our shared system of justice works," Peters said.
He said New Zealand would continue to work with the OPCW and other countries to strengthen the ban on chemical weapons.
Prosecutors said there is enough evidence to charge Alexander Petrov and Ruslan Boshirov with offences including conspiracy to murder in the Novichok attack on ex-Russian double agent Sergei Skripal and his daughter Yulia in March.
In a statement that will deepen the diplomatic crisis between the two countries, May told MPs on Wednesday afternoon that intelligence provided by UK agencies indicates the two Russians responsible for the Salisbury attack are officers of Russia's GRU military intelligence service.
"This was not a rogue operation," May said. "It was almost certainly also approved outside the GRU at a senior level of the Russian state."
The Crown Prosecution Service now faces a battle to bring the case as Russia does not allow the extradition of its own nationals. A European arrest warrant for the two men - who police think were travelling under aliases and are now back in Russia - has been obtained.
Scotland Yard said the military-grade nerve agent was brought into the UK in a fake bottle of Ninna Ricci Premier Jour perfume, which had been designed as a specially-made poison applicator.
It is believed that it was later found by Charlie Rowley before he and his girlfriend, Dawn Sturgess, became indirect casualties of the poisoning. Sturgess died just over a week later.
Neil Basu, Assistant Commissioner of the Metropolitan Police, said it is likely the suspects were travelling under aliases and that Petrov and Boshirov are not their real names.
He said the pair, who are believed to be aged around 40, had been to the UK before on the same passports and had "travelled extensively on them in the past".
Detectives believe the front door of Skripal's Salisbury home was contaminated with the military-grade substance on Sunday, March 4. Basu said CCTV shows the two suspects in the vicinity of the property on that date.
Hours later, the men left the UK on a flight from Heathrow to Moscow - two days after they had arrived at Gatwick.
Releasing a series of CCTV images of the men in Britain, Basu asked witnesses to come forward to establish their real identities.
Russian media reports suggest Boshirov is a 40-year-old Moscow State University graduate who was living in the capital.
He was born in Dushanbe - the capital city of Tajikistan - before moving to Russia where he studied hydrology of the land in the geography department of the university, completing his degree in 2004, according to Fontanka, citing a Facebook profile matching his details.
Boshirov's latest listed address is said to be in Moscow, but less is known about Petrov, other than he is 39.
The Russian site reported a person matching his name and date of birth was on the employees list of an immunobiological manufacturer with links to Russia's Ministry of Health.
Together, the pair are said to have travelled to Milan, Geneva, Amsterdam and Paris several times since September 2016, when Fontanka claims their fake passports were created.
They also travelled to London from between February 28 and March 5 last year, according to the Russian site, 12 months exactly before the Skripals were found poisoned in Salisbury.
They stayed in the two-star City Stay Hotel, in Bow, east London, during their stay in the UK. Officers searching their room on May 4 discovered traces of Novichok, but Scotland Yard said there is no risk to other guests.
The announcement of criminal charges will deepen the rift between Britain and Russia, after the nerve agent attack sparked a wave of diplomatic expulsions by the UK and its allies.
As the news broke, the Russian foreign ministry tweeted a video mocking May's dancing in South Africa. It later said that the names released by Britain "do not mean anything to us".
British authorities believe that several Russians are thought to have been involved in the attempted murders - which also led to 44-year-old Dawn Sturgess becoming an indirect casualty of the poisoning.
It is understood that the suspected perpetrators were identified through CCTV footage that was cross-checked with border entry data.
Sturgess died in July, with authorities believing she and Rowley picked up a discarded vial containing the substance.
The pair fell ill on June 30 in Amesbury, near Salisbury.
Police believe it is linked to the poisoning of the Skripals, who were discovered slumped on a bench on March 4 and have since been discharged from hospital.
Theresa May: 'This was not a rogue operation'
Prime Minister Theresa May told the Commons that CCTV evidence "clearly" places the two Russians in the vicinity of the Skripals' house shortly before the attack on them.
She said: "This hard evidence has enabled the independent Crown Prosecution Service to conclude they have a sufficient basis on which to bring charges."
May told MPs that investigations have concluded the two suspects are members of the GRU, Russia's military intelligence service.
May said: "The GRU is a highly-disciplined organisation with a well-established chain of command. So this was not a rogue operation. It was almost certainly also approved outside the GRU at a senior level of the Russian state."
May said Russia had replied with "obfuscation and lies" when asked to account for what happened, including claiming she had invented Novichok.
She added: "Their attempts to hide the truth by pushing out a deluge of disinformation simply reinforces their culpability."
May said: "The actions of the GRU are a threat to all our allies and all our citizens.
"On the basis of what we have learnt in the Salisbury investigation and what we know about this organisation more broadly, we must now step up our collective efforts specifically against the GRU.
"We are increasing our understanding of what the GRU is doing in our countries, shining a light on their activities, exposing their methods and sharing them with our allies, just as we have done with Salisbury.
"Together with our allies we will deploy the full range of tools from across our national security apparatus in order to counter the threat posed by the GRU."
May told MPs that the CPS did not have a policy of requesting extradition from nations who had constitutions barring the possibility.
She added: "If these two individuals step outside Russia then we will take every step possible to ensure that they are detained and brought to face justice here."
The Prime Minister, in response to calls for a stepping up of sanctions, said: "We will indeed be stepping up our activity across the broad range of our capabilities and what is available to us across our national security apparatus."
May added that around 250 detectives had trawled through 11,000 hours of CCTV footage to identify the attackers and had taken more than 1400 statements.
"Working around the clock, they have carried out painstaking and methodical work to ascertain exactly which individuals were responsible and the methods they used to carry out the attack."