Theresa May is scheduled to inform a summit of EU leaders in Brussels that they need to stay united against the threat that Russia poses to every European democracy.
The prime minister is to soon state that the attack of the nerve agent, Salisbury, illustrates that Moscow does not have respect for established international laws.
The senior official from Whitehall stated that Russia had "shown itself to be a strategic enemy not a strategic partner".
Also set to decide if the terms for a 21-month Brexit transition period will be agreed upon, are European leaders.
May, who won't be around when many other EU leaders talk about Brexit on Friday , is to brief her associates on Thursday on the alleged poisoning of Sergei Skripal, former Russian spy, and his daughter located in Salisbury.
Expected to take on conclusions that decisively stand against the attack, which say that the Russian State deserved blame for, of which is denied by Russia.