British Prime Minister Theresa May will urge European Union leaders to unite and condemn Russia as leaders of the bloc's 28 nations meet Thursday in Brussels.

May is seeking a strong statement against President Vladimir Putin after the poisoning of a former Russian double agent and his daughter in England. Britain blames Moscow for the nerve-agent attack, while Russia insists it's not responsible.

In the wake of the attack Britain has called Russia a growing threat to Western democracies.

EU foreign ministers expressed "unqualified solidarity" with Britain on Monday, but May is hoping for a more strongly worded statement that explicitly condemns Russia.

EU Council President Donald Tusk is seen by the U.K. as supportive, and said Wednesday that Europe must "reinforce our preparedness for future attacks." But British officials are irked that another EU chief, European Commission President Jean-Claude Juncker, congratulated Putin on his victory in Sunday's presidential election in Russia.

The attact on the Skripals has sent tensions between London and Moscow worsen to Cold War levels. The two countries have expelled 23 of each other's diplomats and engaged in an acidic war of words.

On Wednesday, British Foreign Secretary Boris Johnson said it was "emetic" — vomit-inducing — that Putin is rejoicing over hosting the soccer World Cup. Russia retorted that Johnson was "poisoned with venom of malice and hate."

Brexit is also on the agenda at the two-day summit that starts Thursday. Britain hopes the EU will sign off on the terms of the U.K.'s departure next year and green-light talks on future relations.