The EU pressed Russia to reinforce protection of the Estonian embassy in Moscow for it has been besieged by activists protesting the decision to remove the World War II memorial from center of Tallinn.
"We strongly urge the Russian authorities to implement their obligations under the Vienna Convention on diplomatic relations," said European Commission spokeswoman Christiane Hohmann.
She told reporters a delegation of EU ambassadors was seeking a meeting as soon as possible with the Russian Foreign Ministry to pass on the message.
"The violence and the limitations for the Estonian embassy in Moscow have raised, of course, of European solidarity," Hohmann said.
Estonia's ambassador in Moscow Marina Kaljurand said Wednesday that pro-Kremlin youth activists tried to attack her as she tried to hold a news conference and that computer vandals with Kremlin Internet addresses hacked Estonian government Web sites.
Estonia's Foreign Ministry quickly issued a statement in protest.
"Physical attacks on the Estonian Republic diplomatic representative are unprecedented and absolutely unjustifiable," the ministry said in a statement. "The events clearly show that Russian authorities are blatantly violating the Vienna Convention."
Hohmann said the EU in Moscow would insist that Russia respect that 1961 treaty, which regulates diplomatic relations and commits nations to protect embassies and diplomats.
The EU's demand for a diplomatic "demarche" was the strongest action taken by the 27-nation bloc to date in the dispute between Estonia and Russia. The European Commission last week appealed to both sides to seek a peaceful, negotiated settlement over a decision made by Estonia to remove a Soviet war memorial from downtown Tallinn.
Estonian authorities' removal last week of a Soviet war monument from a square in downtown Tallinn provoked riots in the Baltic country, mainly by ethnic Russians.