Senior Nato officials have raised concerns that attempts by Greece to forge a defence pact with Moscow could seriously undermine efforts to present a united front against further acts of Russian aggression.

Maintaining security in eastern Europe and former Soviet Union states is likely to dominate the Nato summit when leaders of the 28-member alliance meet in Warsaw on Saturday.

The summit is the first meeting of Western leaders since Britain’s Brexit vote in last month’s referendum, and Nato leaders are keen to demonstrate the vote does not signal divisions in Europe that could be exploited by the Kremlin.

But in what will be US President Barack Obama’s last Nato summit before he leaves the White House, Nato officials are raising concerns about deepening defence ties between Greece and Moscow which they fear could undermine attempts by Nato to present a united front against Russia.