The rules of conduct between Russia and the West are less clear today than during the Cold War, Estonia’s president has suggested.

Kersti Kaljulaid said she was “worried” that “we do not know” the next steps after Estonia and more than 20 other countries expelled over 100 Russian diplomats in the wake of a nerve agent attack on a former spy in Salisbury.

In the escalating row, Moscow has said it will respond “harshly” to a decision by the US to throw out 60 diplomats it considers to be spies for the Kremlin.

“It is of course worrisome to hear previously during the Cold War period both sides knew the rules,” Ms Kaljulaid told BBC Radio 4’s Today programme. “What are the rules right now, thinking of Salisbury, for example?

“What I am really worried about is indeed that we do not know what might be indeed the next steps. But we know already that nobody expected a military-grade agent would be used on the territory of the UK against people, here, in Salisbury. Is this rules?”

Andrey Kortunov, director general of the Russian International Affairs Council, a think tank established by the Kremlin, told the BBC the expulsion of diplomats risked harming the two sides’ ability to communicate during a crisis.

“During the Cold War we had a pretty robust infrastructure of consultations,” he said. “We had negotiations on arms control, both conventional and strategic arms control.

Russia 'staged a brazen and reckless attack' on UK, says Theresa May

“We had a number of crisis management mechanisms that we could use, so the level of predictability during the Cold War was higher than it is now, both sides knew the rules of the game and I’m not sure it’s the case today.”

But Ms Kaljulaid insisted the West’s response had been the correct one. “I am quite sure these channels of communication will be kept open, but that doesn’t mean we should not retaliate,” she said.

She said despite the escalation in tensions, she did not fear a “hot war” between Russia and Nato because “everybody realises there is nothing to be gained” in such a scenario.

The coordinated move by Britain’s allies represents the biggest single blow to Russian intelligence networks since the end of the Cold War more than 25 years ago.

Theresa May called it “the largest collective expulsion of Russian intelligence officers in history” and hailed the “great solidarity from our friends and partners in the EU, North America, Nato and beyond”.

Countries join UK expelling Russian diplomats over spy poisoning Show all 24 1 /24 Countries join UK expelling Russian diplomats over spy poisoning Countries join UK expelling Russian diplomats over spy poisoning United States Donald Trump has expelled 60 Russian diplomats from the US and closed the consulate in response to the Sergei Skripal spy poisoning. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Great Britain Prime Minister Theresa May confirmed Britain would be expelling 23 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Ukraine Ukrainian president Petro Poroshenko has expelled 13 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Germany Germany's Chancellor Angela Merkel has expelled 4 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning France France's President Emmanuel Macron has also expelled 4 Russian diplomats. Reuters Countries join UK expelling Russian diplomats over spy poisoning Poland Poland's President Andrzej Duda has expelled 4 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Lithuania President of Lithuania Dalia Grybauskaite has expelled 3 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Czech Republic Czech Republic President Milos Zeman has also expelled 3 Russian diplomats. AFP Countries join UK expelling Russian diplomats over spy poisoning Netherlands Netherlands Prime minister Mark Rutte has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Latvia Prime Minister of Latvia Maris Kucinskis has expelled 1 Russian diplomat. Getty Countries join UK expelling Russian diplomats over spy poisoning Estonia Estonia's Prime Minister Juri Ratas has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Croatia Croatia President Kolinda Grabar-Kitarovic has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Italy Italian President Sergio Mattarella has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Canada Canadian Prime Minister Justin Trudeau has expelled 4 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Finland Finland's President Sauli Niinisto has expelled 1 Russian diplomat. Reuters Countries join UK expelling Russian diplomats over spy poisoning Denmark Danish Prime Minister Lars Lokke Rasmussen has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Romania Romania's President Klaus Werner Iohannis has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Norway Norwegian Prime Minister Erna Solberg has expelled 1 Russian diplomat. REUTERS Countries join UK expelling Russian diplomats over spy poisoning Spain Spanish Prime Minister Mariano Rajoy has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Sweden Sweden's Prime Minister Stefan Lofven has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Albania Albanian President Ilir Meta has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Australia Australian Prime Minister Malcolm Turnbull has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Macedonia Macedonia President Gjorge Ivanov has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Hungary President of Hungary Janos Ader has expelled 1 Russian diplomat. AFP/Getty

“Together we have sent a message that we will not tolerate Russia’s continued attempts to flout international law and undermine our values,” she said.

The Russian government said it would retaliate in kind to the “provocative gesture”, with tit-for-tat expulsions probable.

In the sternest move yet against Russia since Donald Trump became president, the White House said it was working with Nato allies to punish Russia for its suspected poisoning of Sergei Skripal and his daughter Yulia and the “unacceptably high” number of Russian spies in the US.

The European Council president Donald Tusk, meanwhile, said expulsions by countries within the European Union were a “direct follow-up to last week’s European Council decision” in which it “condemned, in the strongest possible terms, the recent attack in Salisbury”.

The White House said in a statement: “The United States takes this action in conjunction with our Nato allies and partners around the world in response to Russia’s use of a military-grade chemical weapon on the soil of the United Kingdom, the latest in its ongoing pattern of destabilising activities around the world.”