German Chancellor and leader of the Christian Democratic Union (CDU) Angela Merkel addresses a joint news conference of coalition partners before signing a coalition deal in Berlin, Germany, March 12, 2018. REUTERS/Axel Schmidt

BERLIN (Reuters) - German Chancellor Angela Merkel and British Prime Minister Theresa May agreed on Tuesday that allies should act together to counter “the pattern of aggressive Russian behaviour” after the poisoning of a former Russian double agent in England.

Merkel’s spokesman Steffen Seibert said the German leader had condemned the attack and assured May in a telephone call that she was taking the British government’s views on possible Russian involvement in the attack extremely seriously.

“(Merkel) said it’s up to Russia to quickly provide answers to the British government’s justified questions and to heed the call to completely and immediately lay bare the relevant chemical weapons programme to the Organisation for the Prohibition of Chemical Weapons,” Seibert said.

Moscow has denied any involvement in the poisoning of Sergei Skripal and his daughter Yulia, who have been in a critical condition in hospital since being found unconscious on March 4 on a bench in the English city of Salisbury.

“They (May and Merkel) discussed the pattern of aggressive Russian behaviour and agreed it would be important to act in unison with allies to counter it,” the spokesman for the British prime minister said in a statement.

“They agreed that the international community should coordinate closely as the investigation developed and in the wake of Russia’s response.”

Britain has given Russia until midnight on Tuesday to explain how a Soviet-era nerve agent came to be used against Skripal and his daughter.