More than a dozen European countries have announced they are to expel Russian diplomats in solidarity with with Britain over the poisoning of a former Russian spy.
The group of EU states joined the US, Canada and Ukraine in ordering the removal of Russian embassy and intelligence staff.
"Already today, fourteen member states have decided to expel Russian diplomats," Donald Tusk told a news conference in the Black Sea city of Varna.
"Additional measures, including further sanctions within the common EU framework, cannot be excluded in the coming days and weeks," he said.
Russia has vowed to respond with expulsions of its own, including at least 60 staff from US diplomatic missions in Russia, RIA news agency quoted Russian senator Vladimir Dzhabarov as saying.
An unnamed Foreign Ministry source was quoted as saying: "The response will be symmetrical. We will work on it in the coming days and will respond to every country in turn."
Here is the full list of countries participating in the expulsion:
Estonia
Tallinn is expelling one diplomat.
Poland
Warsaw will expel four Russian diplomats. Polish Foreign Minister Jacek Czaputowicz told a news conference that the diplomats were to leave the country by April 3.
"Showing solidarity with Britain and other countries is the most important thing," Czaputowicz said. "There are diplomatic costs to that but they are worth it."
Lithuania
Three Russian intelligence officers operating under diplomatic cover will be expelled along with sanctions for 21 others. A further 23 will be banned from entering the country.
Latvia
Latvia said it would expel one Russian diplomat.
Romania
Romania will expel one Russian diplomat. "In solidarity with Britain and in accordance with provisions of the Vienna Convention ... the foreign affairs ministry has notified the Embassy of the Russian Federation in Bucharest that a diplomat will be declared persona non grata and is obliged to leave Romanian territory," the foreign ministry said.
Netherlands
The Netherlands will expel two Russian diplomats. The diplomats, who work as intelligence officers at the Russian embassy in The Hague, will have to leave the country within two weeks, the government said.
Denmark
Denmark is expelling two diplomats.
Italy
Two Russian diplomats must leave Italy within a week.
Spain
Madrid has also expelled two diplomats.
Germany
Germany has expelled four Russian diplomats. The foreign ministry said: "After the poisoning attack in Salisbury, Russia is still not cooperating with the investigation."
France
France will expel four Russian diplomats. "In solidarity with our British partners, we have today notified the Russian authorities of our decision to expel four Russian personnel with diplomatic status from French territory within one week," Foreign Minister Jean-Yves le Drian said.
Czech Republic
The Czech Republic said it is removing three staffers from the Russian embassy. Andrej Babis calls the measure an expression of solidarity with Britain.
Finland
Finland will expel one Russian diplomat.
Croatia
Croatia's prime minister says he will expel one Russian diplomat.
Sweden
One Russian diplomat will be kicked out of Sweden in response to the poisoning.
Ukraine
Kiev is expelling 13 Russian diplomats.
Albania
Two diplomats have been told to leave by Albania.
Hungary
One diplomat was ordered out by the government in Budapest.
UK
Britain expelled 23 Russian diplomats and their families last week.
Non European states taking part:
US
The White House says 60 Russian diplomats will be expelled as well as the closure of the Russian consulate in Seattle, which will "make the United States safer", it said.
Canada
Canada says it is expelling four Russian diplomats. Foreign Minister Chrystia Freeland says the nerve agent attack carried out on the soil of Canada's close ally is despicable and potentially endangered the lives of hundreds of people. Three applications by the Russian government for additional diplomatic staff will now be denied.
