The UK has called for an urgent meeting of the UN Security Council to discuss the poisoning of a former double agent in Salisbury, the Foreign Office says.
Russia failed to respond to a midnight deadline set by Theresa May to explain how a Russian-made nerve agent was used on Sergei Skripal and daughter Yulia.
The prime minister is set to announce a series of measures against Russia before MPs later.
Russia said it had “no motive” in the attempted murder of the pair.
The Kremlin, which has consistently denied involvement, said any steps by the PM would lead to “retaliatory measures”.
The Foreign Office said the incident in Salisbury on 4 March, which left the Skripals critically ill, “follows a well-established pattern of Russian state aggression”.