Foreign Affairs Minister Chrystia Freeland announced Monday that four members of Russia鈥檚 diplomatic staff working at the Embassy of the Russian Federation in Canada and at the Consulate General of the Russian Federation in Montreal are being removed from Canada, and three applications for additional staff are being denied.

"The four have been identified as intelligence officers or individuals who have used their diplomatic status to undermine Canada's security or interfere in our democracy," Freeland said in .

Freeland said the move is in 鈥渟olidarity鈥� with the United Kingdom over the March 4 nerve agent attack in Salisbury on former double agent Sergei Skripal and his daughter, both of whom remain in hospital in critical condition.

"The nerve agent attack in Salisbury, on the soil of Canada's close partner and ally, is a despicable, heinous and reckless act, potentially endangering the lives of hundreds," Freeland said.

Freeland also blasted the use of a nerve agent as 鈥渁 clear threat to the rules-based international order and to the rules that were established by the international community to ensure chemical weapons would never again destroy human lives.鈥�

"This is part of a wider pattern of unacceptable behaviour by Russia,鈥� Freeland explained, 鈥渋ncluding complicity with the Assad鈥� regime, the annexation of Crimea, Russian-led fighting in eastern Ukraine, support for civil strife in Ukraine, Georgia, Moldova and other neighbouring countries, interference in elections, and disinformation campaigns.鈥�

According to the , Justin Trudeau and U.S. President Donald Trump spoke about the expulsions via telephone Monday.

鈥淭he leaders discussed measures taken by Canada and the United States to support our common ally against Russia in response to the egregious nerve agent attack in Salisbury, United Kingdom,鈥� the PMO said in a statement.

In total, 21 countries -- including the U.K., U.S., Germany and France -- have expelled 135 Russian diplomats since the attack.

The Russian government has repeatedly denied any involvement.

In a , the Embassy of the Russian Federation in Canada condemned Ottawa鈥檚 decision to expel its diplomats as 鈥渉ighly deplorable and outrageous.鈥�

The statement also decried the U.K.鈥檚 accusations regarding Skripal as 鈥渢otally baseless鈥� and said that by expelling Russian diplomats, Canada was 鈥渙bediently鈥� following the U.S. and U.K.鈥檚 鈥渄angerous confrontational policy.鈥�

鈥淭his unfriendly move under false and biased pretext delivers yet another serious blow to Russian-Canadian relations and will be met with resolve and reciprocity,鈥� the strongly-worded statement concluded.

Russia recently expelled 23 British diplomats in a tit-for-tat move after 23 Russian officials were booted out of the U.K. It remains to be seen how Moscow plans to retaliate against Canada.

Speaking to reporters before question period Monday, Minister of Transport Marc Garneau offered additional details, saying three of the expelled diplomats worked at the Russian consulate in Montreal while the fourth worked at the Russian embassy in Ottawa. All will be forced to leave Canada within the next ten days, Garneau added.

鈥淭hey have been watched for some time,鈥� he said, speaking in French.

Appearing alongside Garneau, Minister of Public Safety and Emergency Preparedness Ralph Goodale described the nerve agent attack as 鈥渉orrendous and despicable.鈥�

鈥淲e believe that the response is perfectly appropriate to demonstrate Canada's strong disapproval of Russia's likely involvement in the situation in Salisbury, standing with the U.K., standing with other countries to make it abundantly clear that this behaviour is unacceptable,鈥� Goodale said.

Goodale, however, declined to explain how the expelled diplomats were working to undermine Canada鈥檚 security and democracy (a point made in Freeland鈥檚 statement about the expulsions), saying only that Canada is 鈥渧ery alert to the activities that we consider to be unacceptable.鈥�

鈥淚 don鈥檛 discuss operational matters,鈥� Goodale added. 鈥淏ut you can be sure that all of our security agencies and police agencies have done their job and they've done it in an exceedingly focused and accurate manner.鈥�

Following question period Monday afternoon, Minister of National Defence Harjit Sajjan offered pointed criticism of Russian-backed incursions into neighbouring territories such eastern Ukraine, the Crimean Peninsula and Georgia.

鈥淲e've stated many times that we're going to protect Canadians and especially when it comes to democratic institutions鈥� and these folks are using their diplomatic status to take action here,鈥� Sajjan said. 鈥淲e, we're not going to allow these individuals diplomatic status to be able to do the type of things that they do to undermine anything in Canada. Canadian security is the number one priority for us.鈥�

With files from The Associated Press