The National Party says the Government's latest statement on the Salisbury nerve agent attack is unacceptable especially compared to other countries.

Foreign affairs spokesman Todd McClay said it was embarrassing for its failure to condemn Russia.

"This attack was an appalling, violent breach of the sovereignty of one of New Zealand's closest friends," said McClay.

"The Government's written statement on this violent attack falls woefully short and is embarrassing.

"The Prime Minister needs to tidy this mess up quickly and explain why her Government continues to be at odds over its Russia policy."

However, Prime Minister Jacinda Ardern on Friday upgraded the bland comments made by Peters, but not before a visiting British Minister Mark Field, had expressed the hope in Stuff that Ardern and Peters would be able to condemn "in unequivocal terms" what had happened.

The investigation has brought attempted murder charges against two named Russian intelligence officers it believes were responsible for the attack in March against a former Russian agent, Sergei Skripal and his daughter Yulia. It concluded that the operation was almost certainly approved as a high Government level.

Foreign Minister Winston Peters issued a statement on Thursday simply welcoming the conclusion of the British investigations following a statement by British Prime Minister Theresa May to Parliament last week.

"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' comments contrasted with statements of condemnation including on from Australia's Foreign Minister Marise Payne: "Australia shares the UK's anger and outrage at this dangerous and deliberate act by Russia…we are in lockstep with the UK on the importance of holding Russia to account and reaffirm our support for calls on Russia to fully disclose the extent of tis chemical weapons programme."

The leaders of France, Germany, the United States, Canada and Britain issued a joint statement saying they had "full confidence" in the British assessment.

After an intelligence briefing, Jacinda Ardern's office sent the following statement to media organisations asking for comment:

"The Government has confidence in the UK's investigation. It confirms that the two suspects were officers from Russian military intelligence. Given the clear chain of evidence produced by the UK, the New Zealand Government supports the UK and the international community in bringing this matter to court.

"New Zealand condemns any use of chemical weapons, whether it is in Syria or the streets of the UK. New Zealand believes all states must adhere to obligations under international law, including in respect of chemical weapons." 

"While there are a range of issues on the agenda at [UN General Assembly], I expect this will form the backdrop to a number of discussions with partners."

Peters was widely condemned when the attacks first happened for issuing a bland statement that refused to condemn Russia and was out of step with like-minded countries.

Under pressure Ardern and Peters issued a stronger statement.