It's estimated that thousands of foreigners have answered Ukrainian President Volodymyr Zelenskyy's call to defend Ukraine. What ramifications could that have?

On February 27, three days into the war in Ukraine, the country's foreign minister, Dmytro Kuleba, took to Twitter to echo a statement from the president's office and launch an appeal for foreign citizens to join Ukrainians in the fight against the Russian army.

On March 5, the president's office announced that a website had been launched to guide foreign nationals through the application process to join the International Defense Legion of Ukraine.

The website provides step-by-step instructions on how to join up.

How many have joined so far?

While reliable numbers are hard to come by, it's believed that thousands of foreign nationals have already rallied to the Ukrainians' cause.

"Very rough figures put it at around 20,000. The majority of them are European and North American. There are 500 from Belarus and also some Japanese volunteers," Ed Arnold, a research fellow for European Security at the Royal United Services Institute, a London-based think tank, told DW.

The Kyiv Independent, an English language Ukrainian media outlet, posted an update on Twitter on March 7.

Some German media outlets say that up to 1,000 German nationals are believed to have traveled to Ukraine. In response to a request for a comment, a German Defense Ministry spokesman said: "The Federal Ministry of Defense has no knowledge about this along the lines of your inquiry."

At a government press conference on Wednesday, Maximilian Kall, a spokesperson for the Federal Interior Ministry, said he could not confirm the figure of 1,000.

"People travel freely within the Schengen area. We assume that they are Ukrainians or at least people with a German-Ukrainian background," he said.

As far as concerns go, regarding the participation of German right-wing extremists, Kall said "the security authorities have this on their radar. They are trying to prevent departures through targeted measures. We know of only a very small, single-digit number of German right-wing extremists who have left."

Background and experience

So who are the foreign nationals joining the war? What kind of background do they have? While the term "foreign fighters" is being used ubiquitously, it's more accurate to describe them as volunteers.

"First of all, they're foreign volunteers because they're joining a state. It's a state mobilization. A foreign fighter is someone who joins an insurgency, a rebellion and non-state actors," Kacper Rekawek, a postdoctoral fellow with the Center for Research on Extremism (C-REX), told DW.

As far as their background goes, it's a mixed bag. Some of those signing up have little to no military experience.

"I'm seeing some of these groups and some of these guys are absolutely green," Rekawek said.

Those without military experience are likely to be assigned logistical tasks such as transporting supplies or personnel to the front lines.

"Someone with a Category C license, for example, driving trucks is probably a better use of his experience and skills than fighting on the front-line. Where they go depends where they could backfill the Ukrainian units. The difficulty of that is they might obviously not speak Ukrainian so they'll probably be nationally put into teams. So all the UK volunteers would form a UK unit," Arnold, explained.

The quality of those who want to fight is likely to differ from case to case. There will be those who have no military experience and will be required to pick up the basics, such as weapons handling, in a matter of a few days.

Even for those vets who have been in combat situations before, this is a completely different experience.

"This is a state-on-state conflict. I have reports from veterans on the ground who say they've shot more ammunition in four days than they did in four full tours of Iraq and Afghanistan. This isn't the same type of conflict that they're used to," said Arnold, who was an infantry officer within the British Army and served in Afghanistan.

Is there a vetting process?

Even at the best of times, performing a thorough background check on someone who wants to join the army can be taxing. Doing so in a full-blown war is almost impossible.

"Ukraine does not have 20 million officers waiting for them. But there is a process to work, and I think the process will continue even after their arrival there. They will be kind of watched on the ground, because the last thing Ukraine needs is foreigners causing trouble," said Rekawek, who has conducted research and published extensively on Western extremist fighters in Ukraine.

That concern stems from Ukraine's recent history and experiences. The presence of foreign fighters in Ukraine, including those with extremist backgrounds, is indeed nothing new. Since 2014, it's believed that over 17,000 fighters from over 50 countries have fought on both the Russian and Ukrainian sides in the Donbas war.

However, as Rekawek explains, the picture is somewhat different this time. While it's important to monitor intelligence on individuals with an extremist background who may be preparing to join, the current situation on the ground tells a different story.

"I have it from the Azov regiment [a right-wing extremist paramilitary group] itself, who told me that 20 were facilitated by Azov to deploy on the front lines. So 20 out of 20,000 foreign nationals who are apparently on the move," he said.

The nature of this conflict, a state-on-state war, is also seen as a mitigating factor in terms of the type of foreign nationals who are willing to risk their lives.

"The skills most in demand now in Ukraine require previous military training, handling specific equipment, or organizing civil resistance. It is my understanding that persons possessing such skills and willing to risk their lives and willing to travel to Ukraine would be less likely to be of extremist convictions," Egle E. Murauskaite, a senior researcher and simulations designer for the ICONS Project with the University of Maryland, told DW via email.

Is it legal?

One question that's been popping up again and again, is whether it's actually legal for foreign volunteers to join the war. Over the past few days, some European and Baltic countries, such as Lithuania and Latvia have passed emergency legal measures allowing individuals to join the war.

"In addition, Ukraine had also passed regulations a couple of years back that allowed foreign fighters to become citizens within a few months of applying and thus officially join the Ukrainian side as Ukrainian citizens," said Murauskaite, who is currently based in Lithuania, where she's responsible for high-level political-military crises simulations in Europe.

The UK's official position is a little more opaque. Foreign Minister Liz Truss said recently that "people can make their own decision, only for ex-Attorney-General Dominic Grieve to point out that it is illegal for British citizens under the Foreign Enlistment Act of 1870.

That law, however, was conveniently ignored for the estimated 3,000 Britons who fought in the Spanish Civil war from 1936-1939.

Asked to comment about the current situation, a UK Foreign Office spokesman told DW: "We advise against travel to Ukraine and anyone who travels to conflict zones to engage in unlawful activity, should expect to be investigated upon their return to the UK."

As Arnold explains, certain laws could apply for those returning depending on how they've conducted themselves in Ukraine.

"But that won't be a deterrent. They believe that if they go over there and do a good job which is broadly in line with their national policies they wouldn't be prosecuted, or that if they were charged the sentence would be proportionate."

From Deutsche Welle Newsfeed