In an emotional video posted to his Telegram channel, Zelensky referred to the “international legion” of 16,000 foreign volunteers he has sought to “join the defense of Ukraine, Europe and the world.” The country earlier this week temporarily lifted visa requirements for foreign volunteers who wish to enter the country and join the fight against Russian forces.

“We have nothing to lose but our own freedom,” Zelensky said, noting that Ukraine’s international allies are sending the country’s arms supplies each day.

While foreign citizens have been fighting in Ukraine since 2014, when Russia-backed separatists seized parts of the Donbass region, experts who track foreign fighters say this push is a step far beyond that in ambition. Experts have warned that traveling to Ukraine with no military training is dangerous.

It remains unclear where 16,000 volunteers are coming from, and Zelensky did not expand on the topic in his video. So far, most of the foreign fighters in Ukraine are from other post-Soviet states like Georgia and Belarus. But media reports suggest they’re from countries such as Japan, Britain and the United States.

Ukraine’s Ministry of Defense echoed Zelensky’s call for foreign volunteers on Facebook, saying it was looking for people with combat experience who have “citizenship other than Ukrainian, but … are standing with Ukraine against [the] Russian invasion.”

“This is [the] time to act!” wrote the General Staff of the Armed Forces of Ukraine. “Join the International Legion of Territorial Defense!” The ministry added, “Do not lose your chance to be part of the bravest Armed Forces!”

The president’s claim comes as Russian troops have seized a key government building in the Black Sea port of Kherson, a Ukrainian official said Thursday, as Moscow tightened its grip on Ukraine’s southern coastline. Russian state media said Russian forces have taken Kherson, a city of nearly 300,000, although British intelligence said Thursday the military situation there remains unclear.

Ukraine has defied the odds to hold a number of cities under fire at a time when more than 1 million people have fled the country since the Russian invasion began, according to data from the United Nations refugee agency — an exodus that is set to become Europe’s worst humanitarian crisis this century.

Zelensky’s statements regarding the foreign volunteers came days after Oleksiy Danilov, the secretary of Ukraine’s National Security and Defense Council, said a recent alleged assassination plot against the Ukrainian president was foiled over the weekend.

The push for foreign volunteers began last weekend when Foreign Minister Dmytro Kuleba tweeted that anyone interested in participating should contact Ukraine’s diplomatic missions in their respective countries.

“Together we defeated Hitler, and we will defeat Putin, too,” Kuleba wrote Sunday.

Since then, countries like Latvia have voted unanimously to allow their citizens to fight for Ukraine, while leaders in nations such as Denmark and Canada have warned of the dangers but are not stopping their residents from making the individual choice to fight against Russia.

While it is legal for U.S. citizens to join foreign militaries in certain conditions, the State Department has advised that American citizens would be in violation if they were “recruited or hired” while still in the U.S., under a Supreme Court decision.

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In the U.K., British Foreign Secretary Liz Truss and British Defense Secretary Ben Wallace have disagreed on whether it was appropriate for civilians to travel to Ukraine to fight in the war.

The risks of being a foreign volunteer remain extraordinary, with cycles of intense fighting and shelling leading to deaths and injuries across Ukraine.

Ukraine’s General Staff of the Armed Forces said Thursday that those interested in fighting for the country against Russia could apply by going to their Ukrainian embassy, or calling or emailing them. Once their application is processed, they will be given assistance on routes to arrive in Ukraine.

“Upon arrival in Ukraine at the collection point, sign a contract and together with soldiers from other countries and Ukrainian soldiers to go to fight against the Russian occupation forces within [the] joint multinational effort,” they wrote on Facebook.

Despite the dangers and risks, some foreigners are not deterred from volunteering in the fight. Dozens of Japanese men, mostly former members of the Self-Defense Forces, have applied to fight in Ukraine, according to the Tokyo newspaper Japan Today. The Times in the U.K. reported that “hundreds of Britons” have written to their Ukrainian embassy wanting to sign up for the fight.

Some in the U.S. and Canada are also signing up in New York City. Christian Gonzalez, of Yonkers, N.Y., told the New York Daily News that signing up to fight with the Ukrainians was “a no-brainer.”

“They have a bully that’s bullying people around him,” said Gonzalez, 35, of Russian President Vladimir Putin. “Why not fight for a greater cause? Even if it’s just pulling people out of rubble. Even if it’s just aiding. It’s history in the making.”

Thousands of miles away, Zelensky praised Ukrainians for fighting back against Putin’s forces, while slamming the Russian president a week into the invasion.

“If someone thinks that, having overcome all this, Ukrainians, all of us, we will get scared, break down or give up — he simply does not know anything about us,” Zelensky said, calling on Putin to “go home.” “He knows nothing about Ukraine. And he has nothing to do here.”

Zelensky added, “Go save your own Russian speakers. Not all over the world — but in your own home.”