Ukrainian academic Nazar Danchyshyn may not have much fighting experience, but to help his country since the start of the war he has deployed his knowledge of language and poetry.

Twice a week, he flips open his laptop for online classes to help fellow countrymen in the former Soviet nation perfect their Ukrainian speaking skills.

"If we all speak Ukrainian in the future that would be a very powerful weapon against aggression," the 30-year-old researcher and poet said.

A sizeable minority of Ukrainians speak Russian as their mother tongue, and many more are fluent, brought up under Moscow's cultural influence, especially in the east and south of the country.

But in recent years, increasingly more people have decided to shift linguistic identity in rejection of Russia's politics.

Since President Vladimir Putin invaded Ukraine in late February, under the pretext of "de-nazifying" its neighbour and protecting Russian speakers there, the trend has soared.

In the western city of Lviv, where the national language is predominant, a group of academics offers free lessons online to those wishing to brush up on their Ukrainian speaking skills.

Organisers say 1,000 people signed up in just three days, and they have so far only managed to find enough tutors for around 800.

Danchyshyn, who was also a guitar player in a band before the war, is one of those teachers.

"People remember that their grandparents and great-grandparents spoke Ukrainian, and then their families switched to Russian" under the Soviet Union, he said.

"Many wanted to return to their native language."

The war in Ukraine has killed thousands and displaced millions at home and abroad over the past seven weeks.

With mounting evidence of likely Russian war crimes, US President Joe Biden on Wednesday accused Moscow of "genocide".

"It's become clearer and clearer that Putin is just trying to wipe out the idea of even being able to be a Ukrainian," the president said.

The conversation classes Danchyshyn gives are online, but organisers say the content is roughly inspired by language textbooks from the Lviv Polytechnic National University.

Twice a week, Nazar Danchyshyn flips open his laptop for online classes to help fellow countrymen perfect their Ukrainian speaking skills
Twice a week, Nazar Danchyshyn flips open his laptop for online classes to help fellow countrymen perfect their Ukrainian speaking skills AFP / Yuriy Dyachyshyn

In their pages appear images of Ukraine's national hero, 19th-century poet Taras Shevchenko, or modern role models such as Oksana Lyniv, a music conductor from Lviv.

Volodymyr Krasnopolsky, a 52-year-old Russian-speaking academic from the eastern city of Lugansk, is one of Danchyshyn's students.

After pro-Moscow separatists seized control of Lugansk in 2014, he moved to the small eastern city of Rubizhne.

But the city was hit by a missile on February 24, and he and his daughter -- a medic student -- spent two weeks sheltering in a basement before they managed to flee westwards.

"There were people of different origins in the bomb shelter with us, but they all felt like Ukrainians," he told AFP via text message.

"Learning Ukrainian is very important to me because I'm showing the aggressor that I'm a Russian-speaking Ukrainian from a Russian-speaking family, but I don't need his protection. I have my own country," he added.

"I believe that the Ukrainian nation is being formed today, regardless of people's origin," he said.

Yuliya, a school principal and maths teacher, said she had joined the course after the conflict forced her to escape bombardment on Ukraine's second city Kharkiv near the Russian border.

"I plan to return home as soon as possible," said the 51-year-old, who teaches in Ukrainian but speaks Russian in her daily life.

But "now is a good time for self-development."

"I'm fluent in reading and writing in Ukrainian, but I struggle with speaking," she explained, without giving her surname.

Under the grand ceiling of the Lviv polytechnic, passionate Ukrainian language advocate and one-time lawmaker Iryna Farion said initiating the free classes was part of "the constant struggle of Ukrainians for the right to be Ukrainian".

Her eyes welled up as she recounted reports that Russians in the southern town of Melitopol had tried last month to force officials to switch the school curriculum to Russian.

"If we do not defend our language, Putin will come here, right into this very building," she said.

As well as the online classes, she said she was planning to give Ukrainian lessons to the parents of displaced children enrolled at a local school to help them follow their homework.

"This is my frontline. My bullets are words," she said.