"It is an assault on United Kingdom sovereignty and any such use by a State party is a clear violation of the Chemical Weapons Convention and a breach of worldwide law".
They demanded Moscow "address all questions" related to the attack against former Russian spy Sergei Skripal, which they said amounted to a "breach of worldwide law".
But that gathering is a week away and it appears unlikely that they will have anything concrete to put forward by then, with the next European Union leaders' meeting in June now the new deadline.
French President Emmanuel Macron and German Chancellor Angela Merkel pledged on Friday to formulate a roadmap for euro zone reform by June, but they may struggle to find common ground on further change in Europe.
Merkel said that the UK's European allies would ask the worldwide organizations to intervene, while "we adopt the best possible response to this attack".
Macron called for ambitious reforms of European Union institutions in September, but he was waiting for the response from Germany.
Macron has called for a major reform drive to reinvigorate the EU, including a common eurozone finance minister and budget, but some European leaders have expressed reservations. "But Germany and France have also achieved a lot in the past and now we have the firm intention to do that again", Merkel said as she met Macron for the first time since she formed a new coalition government.
"This is our task by June: on the eurozone, on migration policy, defense, trade, research, education and large areas that we have been able to set out - we will propose a clear, ambitious roadmap for this re-foundation by June".
"We are not always on the same page".
The chancellor said that her new coalition with the Social Democrats (SPD) would mark a new breakthrough for Europe, and that it came about largely as a response to the situation in France. I am determined to get there and I think we can do it.