Sergey Lavrov, the Russian Foreign Minister, stressed that a military confrontation between the nuclear powers must be avoided.
Ukraine ordered, on Wednesday, to "tighten security measures" for all its embassies, after an employee at its mission in Madrid was slightly injured when a letter bomb exploded.
Ukrainian Foreign Ministry spokesman Oleg Nikolenko said on Twitter: "Ukrainian Foreign Minister Dmytro Kuleba ordered to strengthen the security of all Ukrainian embassies, and also called on the Spanish authorities to urgently investigate this attack."
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