António Costa, the president of the European Council, has defended his surprise decision to open a diplomatic channel with the Kremlin to assess whether conditions exist for peace negotiations — a possibility his team concluded is not currently viable.

The issue dominated Thursday’s summit of EU leaders in Brussels.

No clear explanation emerged as to why Costa, who has made maintaining the unity of the 27 a central theme of his presidency, decided it was the right time to reach out to Moscow. Earlier this week, it emerged that his chief of cabinet, Pedro Lourtie, had held several phone calls with a top aide to Russian President Vladimir Putin.

It is understood, although his office did not confirm, that the official was Yuri Ushakov.

"The President explained that he had asked his office to open a diplomatic channel with Russia. The aim was to be ready, when the right moment comes, to defend the EU’s interests. What we are talking about are brief contacts, with no exchange on substance and no negotiations — simply diplomats carrying out diplomatic work," an EU official said.