Lawyers of Ukrainian oligarch Dmytro Firtash, who was detained in Vienna on a Spanish arrest warrant on February 21, are seeking their client's release on bail from a jail in the Austrian capital, according to the Ukrainska Pravda online outlet.

"Firtash should be bailed in the Spanish case soon," the publication quoted an unnamed "representative of the businessman" as saying. Firtash will stay in Vienna due to the fact that his defenders "found a formula for challenging" an Austrian court ruling allowing his extradition to the United States, the source said.

Firtash was detained in Vienna on a Spanish arrest warrant on February 21, shortly after the US request to extradite him over bribery allegations was upheld by the Higher District Court of Vienna. A court in Vienna initially refused to extradite him in 2015.

In 2016, the Anti-Corruption Prosecutor's Office of Spain put Firtash on the international wanted list for alleged money laundering in large amounts.

Crimes allegedly involve tens of millions of euros of criminal origin that were transferred for Firtash through a number of offshore companies in Panama, while some of the funds were invested in Spanish real estate.

Meanwhile, Firtash is wanted in the US for allegedly bribing Indian officials to secure mining licences. The Austrian court accepted the argument of Firtash and his lawyers that the US case was politically motivated, and was aimed at removing the businessman from active participation in Ukrainian politics.

Meanwhile, the pro-Russian Opposition Bloc in Ukraine, which is partly controlled by Firtash, said on February 22 that the Ukrainian aviation authorities have closed the air space for private planes to prevent the businessman from returning to his homeland.

"We attribute this decision to possible return home of the well-known businessman," the Bloc's lawmaker Mykola Skoryk told journalists in the country's parliament. "This situation already took place in 2015, when Firtash was going to visit a congress of Ukrainian Federation of Employers [headed by Firtash at the time]. Radicals together with the authorities did everything to prevent this, they locked [Kyiv] airport."