A Ukrainian pharmaceutical company backed by a prominent Russian-leaning opposition figure has applied for state approval to make Russia’s Sputnik V COVID-19 vaccine, a sensitive move given toxic relations between Kyiv and Moscow.

The two countries have been at loggerheads since Russia’s annexation of Crimea from Ukraine in 2014 and involvement in a conflict in Ukraine’s eastern Donbass region which Kyiv says has killed 14,000 people.

Ukraine’s government has played down the prospects of approving the Sputnik V vaccine quickly, if at all. Foreign Minister Dmytro Kuleba called the vaccine “a hybrid weapon of Russia against Ukraine” in an interview with The Day newspaper.

Ukrainian pharmaceutical firm Biolik said in a statement on its website it had applied to register Gam-COVID-Vac, also known as Sputnik V, in Ukraine. Russia on Saturday floated the idea of holding clinical trials in Ukraine.

Biolik’s application has been promoted by the Ukrainian opposition politician Viktor Medvedchuk, an ally of Russian President Vladimir Putin.

Ukraine’s health ministry did not immediately respond to a request for comment, but Deputy Health Minister Viktor Lyashko was quoted by Interfax news agency as saying Ukraine would only use vaccines that had finished clinical trials. Sputnik V is still undergoing Phase III trials.

Ukrainian President Volodymyr Zelenskiy told the New York Times last month that the vaccine would be used in Russia’s “information war” against Ukraine.

But he was also quoted as saying “…it is impossible to explain to Ukrainian society why not take the vaccine from Russia if America and Europe do not give you the vaccine. It is impossible to explain that to anyone who dies.”

Zelenskiy’s government is looking to secure COVID-19 vaccines from China and the global COVAX scheme for poorer nations to fight the pandemic.