The Russian-Austrian opera soprano Anna Netrebko has given support to east Ukrainian separatists, posing with one of their top political leaders and holding up the flag of Novorossia, a self-declared amalgamation of territory that is seeking independence from Kiev.

Netrebko, who holds dual citizenship, was pictured with the flag during a press conference in St Petersburg over the weekend, where she announced she was donating 1m roubles (£12,000) to the Donetsk Opera Theatre.

“I have a lot of musician friends in Donetsk, we have been writing to each other a lot, and they told me the theatre was sacred for them, and the building had been partly damaged. I decided that I wanted to help as much as I can. I think it’s the right thing to do because art is art, and helps us get through all situations,” Netrebko said.

Donetsk is under the control of pro-Russia separatists, and much of the civilian population has fled after areas of the city were shelled by the Ukrainian army. Fighting in east Ukraine has killed more than 4,000 people since May.

The main opera house building has not suffered but a warehouse where costumes are kept was damaged by shelling. Although many of the singers and orchestra have left town, the theatre plans to put on operas and ballets this season.

Netrebko said she would visit Donetsk and sing at the opera theatre as soon as military hostilities in the region were over. Asked about her views on the conflict, she insisted she was apolitical. “This is politics and I have nothing to do with politics, I just want to support art,” she said.

However, minutes later she held up the Novorossia flag and handed over a cheque to Oleg Tsaryov, a former Ukrainian MP who is wanted by Kiev on charges of separatism. Tsaryov, who is on a list of individuals sanctioned by the EU for their role in events in east Ukraine, styles himself as the chairman of the parliament of Novorossia.

“Donetsk has not surrendered, just like Leningrad did not surrender [during the Nazi siege],” Tsaryov said. “This [donation] is important for us not just because it’s money, but because it is support for us.”

Netrebko, 43, is one of the most in-demand opera singers in the world, drawing full houses for her performances. She made her name at the Mariinsky Theatre in St Petersburg, whose director, Valery Gergiev, is close to the Russian president, Vladimir Putin. Some of Gergiev’s concerts in the west have been disrupted over his apparent support for the government line on issues such as gay rights.

Netrebko is due to perform in Tchaikovsky’s Iolanta at the Metropolitan Opera in New York in January, and will sing the role of Mimi in Puccini’s La Boheme at the Royal Opera House in London next summer.