Four leaders issue joint statement blaming Russia for the poisoning of Sergei Skripal.
The leaders say there is "no plausible alternative explanation" to Russia being to blame".
The statement follows days of diplomacy by Theresa May.
Statement comes as NATO meets to discuss the crisis.
LONDON — The leaders of United States, Britain, France and Germany have released a joint statement condemning Russia for the poisoning of Sergei Skripal in England last week.
Donald Trump, Theresa May, Emmanuel Macron and Angela Merkel all agreed that there was "no plausible alternative explanation" than that Russia was to blame for the attack.
The leaders called on Russia to "live up to its responsibilities as a member of the UN Security Council," adding that Russia's actions "threaten the security of us all."
The statement marks a significant ramping up of tensions with Russia and comes as members of the NATO council meet to discuss the crisis.
It also follows several days worth of diplomacy by May following an initial reluctance from the French and US government's to publicly attribute the incident to Russia.
It also follows the announcement on Wednesday that Britain will expel 23 Russian diplomats from the UK following the attack.
RELATED: UK investigates nerve agent attack on former double agent Sergei Skripal
Britain is also set to freeze the accounts of individuals close to Russian president Vladimir Putin, as well as suspend all high-level contact with the Russian government.
The joint statement in full
We, the leaders of France, Germany, the United States and the United Kingdom, abhor the attack that took place against Sergei and Yulia Skripal in Salisbury, UK, on 4 March 2018. A British police officer who was also exposed in the attack remains seriously ill, and the lives of many innocent British citizens have been threatened. We express our sympathies to them all, and our admiration for the UK police and emergency services for their courageous response.
This use of a military-grade nerve agent, of a type developed by Russia, constitutes the first offensive use of a nerve agent in Europe since the Second World War. It is an assault on UK sovereignty and any such use by a State party is a clear violation of the Chemical Weapons Convention and a breach of international law. It threatens the security of us all.
The United Kingdom briefed thoroughly its allies that it was highly likely that Russia was responsible for the attack. We share the UK assessment that there is no plausible alternative explanation, and note that Russia's failure to address the legitimate request by the UK government further underlines its responsibility. We call on Russia to address all questions related to the attack in Salisbury. Russia should in particular provide full and complete disclosure of the Novichok programme to the Organisation for the Prohibition of Chemical Weapons (OPCW).
Our concerns are also heightened against the background of a pattern of earlier irresponsible Russian behaviour. We call on Russia to live up to its responsibilities as a member of the UN Security Council to uphold international peace and security.
May today visited the site of the poisoning in Salisbury England to meet local people and those investigating the poisoning.