Russian Foreign Minister Sergei Lavrov said on Friday Russia will expel British diplomats in response to London's decision to expel 23 staff at the Russian embassy in London.
Asked by a Reuters reporter, at a summit on Syria in the Kazakh capital, if Russia planned to expel British diplomats, Lavrov replied: "We will, of course." He did not give any further details.
Britain, the United States, Germany and France jointly called on Russia on Thursday to explain the attack. U.S. President Donald Trump said it looked like the Russians were behind it.
Russia has refused Britain's demands to explain how Novichok, a nerve agent developed by the Soviet military, was used to strike down Sergei Skripal, 66, and his daughter Yulia, 33, in the southern English city of Salisbury.
Skripal, a former colonel in the GRU who betrayed dozens of Russian agents to British intelligence, and his daughter have been critically ill since March 4, when they were found unconscious on a bench.
A British policeman who was also poisoned when he went to help them is in a serious but stable condition.
President Vladimir Putin, a former KGB spy who is poised to win a fourth term in an election on Sunday, has so far only said publicly that Britain should get to the bottom of what has happened.