MOSCOW (AP) — Russia's Foreign Ministry has summoned the British ambassador to Russia for talks in a heightening dispute over a nerve agent attack on a former spy in Britain.

Russia is expected to announce the expulsion of some British diplomats in a retaliatory measure. British Prime Minister Theresa May this week ordered 23 Russian diplomats expelled as part of measures to punish Russia over the March 4 poisoning of former spy Sergei Skripal and his daughter Yulia in the city of Salisbury.

British Ambassador Laurie Bristow is expected at the Russian Foreign Ministry late Saturday morning.

Britain's foreign secretary accused Russian President Vladimir Putin of personally ordering the poisoning. Putin's spokesman denounced the claim.