The first batch of volunteer militants left Belgium Thursday to back Ukraine in the face of Russia, despite official Belgian advice not to go.

According to Ukraine's Embassy in Belgium, seven guys were heading from Brussels to the Polish-Ukrainian border on a coach provided by the Embassy and driven by a volunteer driver.

The foreign militants volunteered after Ukrainian President Volodymyr Zelensky called for foreigners to join an "international brigade" on Saturday.

Around 16,000 foreigners have so far answered the call from some 20 nationalities, Zelensky said Thursday, according to the Reuters news agency.

"They are in the embassy now and they are leaving right now," a Ukrainian diplomat said Thursday afternoon, speaking of the first men from Belgium.

Out of the 70 men who had contacted the Ukrainian Embassy to volunteer, another 18 were expected to follow in the coming days after completing Ukrainian application paperwork and interviews.

Men from Brazil, France, Georgia, Italy, Latvia, Luxembourg, Morocco, and Sweden, many of whom had prior military experience, applied alongside Belgians.

International hotlines have also been established by Ukrainian authorities to assist foreign fighters in joining the front lines.

There were some 400 fighters coming from Sweden, media there said. Another 70 volunteers, including 50 former soldiers, were also coming from as far afield as Japan, Reuters reported.

Many Belarusian volunteers have been fighting against Russia in east Ukraine for years, but their numbers are growing, a Belarusian opposition source who did not want to be identified claimed.

But the Belgian Foreign Ministry's advice is for people not to go. "Our advice is clear: do not travel to Ukraine for any purpose or reason due to the security situation," a Belgian spokesperson told EUobserver.

The Belgian Interior Ministry is studying the legal implications of foreign militants, looking into questions such as: whether volunteers would be committing murder if they killed people in Ukraine, and whether their status would be as prisoners-of-war or civilian captives, were they to be captured by Russian forces.

Volunteers to "the rescue"

The foreign militants will also be operating in an environment where EU and NATO countries, such as Germany, the Nordic states, the Baltic states, and the Netherlands have been supplying small arms, anti-tank, and anti-aircraft missiles, much of which has been delivered across the Polish border before supply routes have been cut.

Russia has threatened NATO states, which meddle in the fight, with retaliation.

The Belgian Foreign Ministry spokesperson claimed that the fact that volunteers were being allowed to travel could in no way be construed as violating NATO's promise to stay out of the fighting.

Russia martial law

Following Ukrainian proposals for an oil and gas embargo, EU foreign ministers are set to debate additional economic measures against Russia at a meeting on Friday.

"There is talk of martial law legislation being introduced Friday," Vladimir Ashurkov, a Russian émigré living in London told EUobserver. "This would be seen as a bad sign" of how the conflict was going for Putin, he said.

Kremlin Spokesperson Dmitry Peskov on Thursday denied the reports.

According to an EU diplomat, if martial law is imposed, it could stop Russians from leaving the country and it could mean media blackouts, fast-track jail sentences for dissidents, and mass military mobilization.

Even as relations with the West deteriorated, some EU countries, notably France, have urged their citizens to leave Russia, citing concerns that European and Russian aviation restrictions, which the West initiated, and counter-sanctions could trap people.