The Russian ambassadors to Poland, Latvia, Lithuania and Estonia were summoned to the foreign ministries of those countries on Monday, Russian news agencies reported.
The RIA news agency cited a spokesman for the Russian embassy to Poland, and a representative of the embassy in Lithuania. TASS referred to unnamed diplomatic sources. The agencies did not give a reason for the summoning.
Russia-EU relations have strained since the March poisoning of Russian ex-spy Sergei Skripal and his daughter Yulia. Britain has expelled 23 Russian diplomats and the Russian government of "unlawful" use of force. Russia responded by expelling 23 British diplomats and threatened further measures.
Former spy Sergei Skripal, 66, and his daughter Yulia, 33, were found unconscious on a bench in the city of Salisbury on March 4 and remain in hospital in critical condition.
British Prime Minister Prime Minister Theresa May said the pair were attacked with Novichok, a Soviet-era military-grade nerve agent. She had asked Moscow to explain whether it was responsible for the attack or had lost control of stocks of the highly dangerous substance.
While Russia has vigorously denied involvement in the attack, Western powers see it as the latest sign of alleged Russian meddling abroad.
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