Foreign Minister Winston Peters has called for an urgent international investigation into Russia's possible involvement in the nerve-agent attack on former double agent Sergei Skripal and his daughter Yulia.

But the New Zealand First leader stopped short of supporting Britain's calls for reprisals if Russia does not provide a credible response to Britain's claims that it was behind the attack.

Peters' statement followed a rare move by the British High Commission in Wellington to brief New Zealand media on the case this afternoon, as part of a worldwide push by British diplomats.

British Prime Minister Theresa May delivered a statement to Britain's Parliament in which she said Russia was highly likely to have been behind the attack and had until Wednesday morning (NZ time] to provide a credible response or it would face reprisals.

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Helen Smith, the Deputy High Commissioner to New Zealand, said diplomats were briefing the New Zealand Government on Britain's conclusion that Russia was "most likely responsible" for the attack on the Skripals.

"We'd certainly be looking not just at a bilateral response but also to what we can do with international partners and through international institutions.

"If we have not received a clear and coherent response from the Russians by the end of Tuesday UK time we will take this as a signal that this was a deliberate act by the Russian state against the UK and we will consider a full range of measures which might include things like sanctions, expelling diplomats et cetera. But those will be discussed further by the British Government and British Parliament before any decisions are made."

Personnel in hazmat suits work to cover a bench at the Maltings shopping centre in Salisbury, England, where former Russian double agent Sergei Skripal and his daughter Yulia were found critically ill. Photo / AP
Personnel in hazmat suits work to cover a bench at the Maltings shopping centre in Salisbury, England, where former Russian double agent Sergei Skripal and his daughter Yulia were found critically ill. Photo / AP
Theresa May today told Britain's Parliament Russia was highly likely to have been behind the attack and had until Wednesday morning (NZ time] to provide a credible response or face reprisals. Photo / AP
Theresa May today told Britain's Parliament Russia was highly likely to have been behind the attack and had until Wednesday morning (NZ time] to provide a credible response or face reprisals. Photo / AP

It is likely as well as bilateral action against Russia, the United Kingdom would take action at the United Nations, including on the Security Council where Russia has a veto power.

On Tuesday night, Peters issued a statement saying the Government had "grave concerns" about the use of a nerve agent in the United Kingdom.

"How this military grade nerve agent was transported from Russia and released abroad is the key issue here, and warrants urgent international investigation," Peters said.

His statement did not refer to the British Government's response and request of Russia for an explanation. It was also silent on whether New Zealand would back any reprisals sought by the United Kingdom if it was not satisfied with Russia's explanation.

However New Zealand would express its view in international meetings and an investigation into the use of chemical weapons should be supported.

"The use of chemical weapons as a tool of war, or for murder or assassination is totally repugnant, and this incident is an affront to global rules and norms."

An advocate for a free trade agreement with Russia, Peters recently said there was no evidence the Russian Government was involved in either the missile strike on MH17 over Ukraine or in interfering in the US election. Russia has denied its involvement in both and investigations and legal proceedings are still underway.

Todd McClay, National Party spokesman on Foreign Affairs, said the Government had to take any request from the UK very seriously.

"The UK is one of our closest friends and if the Foreign Minister's position is at all confused the Prime Minister needs to take responsibility for any decisions herself."

Prime Minister Jacinda Ardern and Peters are due to go to London next month for the Commonwealth Heads of Government meeting where the Russia situation is set to be the main topic of conversation in bilateral meetings with the likes of May and British Foreign Secretary Boris Johnson.

Smith said she was confident Peters shared the UK's values on the rule of law, importance of good governance and rules-based system.

"We have a very good relationship with Winston Peters. He's a very respected operator in international affairs and that will continue. We look forward to a strong, positive conversation with them about this instance."

It is the first use of nerve agents on British soil since World War II.

Smith said while the use of the Russian nerve gas was on British soil, it did not only affect the United Kingdom.

"This is not just a domestic incident. This is part of a pattern of Russian aggression internationally and needs an international response and we are keen to get our message out and work with partners overseas in terms of understanding potential Russian culpability for this act."

She said it was an attack using a nerve agent which injured 24 other people, including a police officer who remained in a serious condition. "People of any nation could have been caught up in it."

She said the briefings around the world were to drive home the serious nature of the attack.

"Russia has had a sustained campaign of aggression internationally. This ranges from the annexation of Crimea through to the murder of Alexander Litvinenko in the UK in 2006, through a whole campaign of cyber espionage, interference in elections and many other things. This has the potential to undermine the international rules-based system which is so important to both the UK and New Zealand."

The Skripals are still critically ill following the attack on March 4 in the southern England city of Salisbury. About 24 others needed medical treatment, including a police officer, and traces of the agent were found at a pub and restaurant visited by the Skripals that day. The nerve agent was identified at Novochok, a military-grade agent developed by Russia.

Skripal was a former Russian spy and informant for Britain's foreign intelligence service.

The British Government believes it was either a direct action by the Russian state or Russia had lost control of its nerve agent programme and allowed it to get into the hand of other agents.