The Czech Republic on Thursday ordered Russia to remove more staff from its Prague embassy, in a growing spat between the two countries.

Last week, Prague expelled 18 embassy staff members, saying they were intelligence officers.

The dispute stems from Czech accusations that Russian spies were behind a deadly explosion at a Czech arms depot in 2014. They claim the spies were also part of a special unit that tried to assassinate a double agent in Britain.

Russia denied the accusations and expelled 20 Czech diplomats last Sunday.

Newly appointed Czech Foreign Minister Jakub Kulhanek announced Thursday that Russia had to match the number of Czech staff in Moscow. This means that by the end of May, about 60 people will have left Prague under expulsion orders.

"We will put a ceiling on the number of diplomats at the Russian Embassy in Prague at the current level of our embassy in Moscow," Kulhanek said. A ministry spokeswoman said the decision included diplomats and other staff.

Earlier in the week, Prague urged NATO and other European allies to take retaliatory action against Russia.

The Russian Foreign Ministry said Thursday it would retaliate for the expulsions.

"At the moment, Prague is on the path to destroying relations," Russian Foreign Ministry spokeswoman Maria Zakharova said at her weekly briefing. "We will respond shortly."

The explosion at the arms depot was initially thought to be an accident. Czech investigators, however, recently revealed they discovered an email that had been sent prior to the blast to "Imex Group," the company that operated the depot. The message asked that two men be allowed to visit the site. The email was sent from an address purporting to be that of the National Guard of Tajikistan, but which was later shown to be fake.

Prague said the two men used the aliases Ruslan Boshirov and Alexander Petrov and that they belonged to Unit 29155 of Russia's GRU military intelligence service.

European Union foreign policy chief Josep Borrell expressed support Monday for the Czech Republic's actions.

"These diplomats have been identified by the Czech intelligence to be Russian military service agents, and the European Union stands united and in solidarity with the Czech Republic," he said.

Relations between Moscow and the West have been strained in recent weeks as Russia deployed military hardware and tens of thousands of troops along the Ukrainian border. The EU called for de-escalation, and on Thursday, Ukraine's president said a Russian pullback was reducing tensions.