"This afternoon, we summoned the Russian Ambassador to Estonia, whom we presented with a diplomatic note stating that the Russian Embassy's military attaché must leave the country," Minister of Foreign Affairs Sven Mikser (SDE) said at a press conference held on Monday afternoon. "His actions are not in line with those agreed upon in the Vienna Convention on Diplomatic Relations."

The foreign minister confirmed that Estonia's decision is part of a coordinated response of EU leaders' March 23 decision regarding Russia's activities and unwillingness to fully cooperate with the U.K. on identifying those responsible for the March 4 nerve agent attack, according to a ministry press release.

"The Salisbury attack is not only a dispute between the U.K. and Russia; it threatens international security and undermines international law," Mikser emphasized. He noted that the nerve agent attack was a serious crime which Estonia has condemned.

"We find it incredibly important to take this deterring step," Mikser said. "It is clear that without a uniform response, such actions will recur."

The Estonian minister also noted that on Thursday he will be proposing to the government that Estonia impose sanctions on the 49 individuals included on the Magnitsky List.

According to Mikser, it is believed in the U.K. that the use of a chemical weapon may have resulted in the exposure of more than 130 people to the nerve agent. He also cited the European Council's stance in which the EU agrees with the U.K.'s assessment that it is very likely that Russia was behind the nerve agent attack.

"We continue to urge Russia to cooperate with the U.K. and the international community to identify the individuals responsible for this crime," Mikser said.

Ambassador: Russia will be quick to respond

Russian Ambassador to Estonia Alexander Petrov, who was summoned to the Ministry of Foreign Affairs at 3 p.m. on Monday, said as he was leaving that he must consult with Moscow, but that he believed that Russia's response will be swift.

Should Russia choose to respond in kind, they may do so by expelling Estonia's Defense Attaché Col. Toomas Peda from Russia.

President Kersti Kaljulaid on Monday commented steps to be taken against Russia in reaction to the poisoning of Sergei Skripal and his daughter Yulia, saying that the EU and NATO's reactions need to take into account more than a decade of events, including the occupation of parts of Georgia.

Other countries also expelling Russian diplomats

The Latvian and Lithuanian Ministries of Foreign Affairs likewise summoned their respective Russian ambassadors on Monday. Latvia is expelling one diplomat, while Lithuania is expelling three along with imposing an immigration ban against 44 individuals.

The U.S. government also announced on Monday that it is expelling 60 Russian diplomats from the country and will demand that Russia close its consulate in Seattle. Among the 60 diplomats to be expelled are 12 who work at the UN, the BBC reported on Monday afternoon.