Around 20,000 international volunteers have traveled to fight Russia in Ukraine, mostly coming from European countries, according to a Ukrainian top official on Sunday. 

"This number is around 20,000 now. They come from many European countries mostly," Ukrainian Foreign Minister Dmytro Kuleba told CNN. "Many people in the world hated Russia and what it was doing in recent years, but no one dared to openly oppose and fight them."

This comes alongside the 16,000 foreign mercenaries whom Zelensky announced will be fighting in Ukraine. 

Zelensky’s remarks came after the Japanese newspaper Mainichi quoted an unnamed source as saying that approximately 70 Japanese volunteers are set to join the ranks of mercenaries in Ukraine's "foreign legion".

Kuleba continued, "So when people saw that Ukrainians are fighting, that Ukrainians are not giving up, many felt motivated to join the fight."

Pointing out that, to Kiev, it was important to receive "sustainable political, economic and military support," Kuleba said that Ukraine needs Washington.

"We need US leadership in this exercise, with special focus on air defense," Kuleba said. 

Since the start of the military operation, Zelensky invited foreigners - including Israelis - to fight alongside the Ukrainian army against Russia. 

The volunteers that applied were able to get through, through Ukrainian embassies in their countries. European countries had mixed feelings about sending so-called "volunteers" - while Denmark has given the green light, British foreign secretary Liz Truss authorized the opportunity but was contradicted by the head of the armed forces Admiral Tony Radakin, who said it was "unlawful and unhelpful" for the British to fight Russia in Ukraine. 

Read more: UK military head: “Unlawful” for Britons to fight in Ukraine