Russia on Monday threatened retaliation after the European Union slapped sanctions on Russian military intelligence chiefs over the nerve agent attack on former Russian spy Sergei Skripal in Britain.

“We reserve the right to take retaliatory measures over this unfriendly step,” the Russian foreign ministry said in a statement.

The European Union introduced sanctions against Igor Kostyukov, the new chief of Russia’s GRU military intelligence, and his first deputy Vladimir Alexseyev.

Kostyukov took over the GRU after the death of his predecessor Igor Korobov last November.

The EU also released the real names of the two agents accused by Britain of carrying out the chemical attack in Salisbury last March, confirming earlier reports identifying them as Anatoly Chepiga and Alexander Mishkin.

Moscow said the claims did not “stand up to criticism.”

“An information campaign unleashed by the British authorities over this case primarily has a domestic agenda,” the Russian foreign ministry said.

“It is telling that its new round coincides with a new crisis in Brexit talks.”

Konstantin Kosachev, chair of the foreign affairs committee of the Russian upper house of parliament, for his part called the introduction of sanctions “an irresponsible decision”.

“The European Union is demonstrating its euro-solidarity, which is used to replace the absence of evidence,” he told Russian news agencies.

“It is strange that this euro-solidarity is being shown towards the UK which is scandalously leaving the EU and which is leaving the EU with the Salisbury scandal one on one.”

He said the Salisbury scandal is capable of “poisoning ties between the EU and Russia for a long time.”

Before the sanctions were announced, Kremlin spokesman Dmitry Peskov said earlier Monday that the new EU measures were unsubstantiated.