Like everyone else, musicians and audience members in Ukraine have been forced to seek refuge underground ever since the Russian invasion began back in February. Svyatoslav Yanchuk's concerts are no different, while they may begin beneath the sky, when the air raid sirens go off they head beneath the earth.

"When the alarm stops, we can return to the stage. When it lasts more than an hour, the concert is called off," said Yanchuk, a percussionist with the Odessa Philharmonic. "It happens almost every concert," he said.

However, in August, Yanchuk will finally be able to play without interruptions on an international trip with the newly created Ukrainian Freedom Orchestra.

Along with dozens of other musicians, Yanchuk will be on a tour of Europe and the United States, which started in Warsaw this week and will include the Proms in London on Sunday.

The orchestra, assembled from musical ensembles in Ukraine and Europe, is the brainchild of Canadian conductor Keri-Lynn Wilson, whose grandparents were from Ukraine.

Wilson was in Warsaw when the war broke out.

"As I witnessed the refugees streaming into Poland, I had a dream of uniting Ukrainian musicians in an artistic force to help them fight for their freedom," she said.

The project quickly took shape with the support of the Polish National Opera in Warsaw and Metropolitan Opera in New York.

Despite never having played together before, the orchestra came up with a concert program in just 10 days.

The concert starts with Ukrainian composer Valentyn Sylvestrov's Symphony No. 7 – a homage to the victims of the war.

There is "no Russian music," according to orchestra members, whose lives and careers have been turned upside down by the war.

"Russia has geniuses but whatever comes from Russian culture is on hold for the moment," said bassoon player Mark Kreshchenskiy.

Kreshchenskiy and his brother Dmytro, a violist, played for the Saint Petersburg Philharmonic Orchestra in Russia for eight years and were there when the invasion began.

"We left Russia in the first days of the invasion. It was hard but there was no other decision to take," Kreshchenskiy told Agence France-Presse (AFP).

The two brothers fled to neighboring Estonia, carrying their instruments.

Ukraine has stopped all fighting-age men from leaving the country under martial law in case they have to be drafted, but some orchestra members have temporary permission to do so.

"I was able to see my 10-year-old daughter again after five months of separation because she is a pupil at the Gdansk Opera" in northern Poland, said Dmytro Ilin, from the Kyiv Philharmonic.

Once the Ukrainian Freedom Orchestra tour is over, Ilin will return to Kyiv – along with percussionist Yevgen Ulyanov, whose son was born when the war broke out.

"My son is waiting for me," he said.

Like many of their colleagues, Ilin and Ulyanov want to continue practising their craft in their native country.

"I have the feeling that we are soldiers of music because we are doing our best at the cultural front," said Nazar Stets, a double bass player and Kyiv resident.

Stets is particularly keen on the Ukrainian repertoire, saying: "It's now the time to play even more Ukrainian music."

"If we don't play our Ukrainian music, nobody will," he said.

Asked if music could really be a weapon, Ilin said: "Since childhood, music has been what we do. We have to act in one way or another."