A Kiev court has started a detention hearing against Roman Nasirov, the controversial head of Ukraine’s powerful tax and customs agency, in what could be a landmark case for the country’s faltering fight with top-level corruption.

Anti-graft prosecutors suspect that Mr Nasirov defrauded the state of some €70 million in tax payments, to the benefit of firms linked to fugitive Ukrainian deputy Oleksandr Onishchenko. Mr Nasirov’s lawyers say he was detained illegally.

The case took several bizarre turns in recent days: Mr Nasirov claimed to have suffered heart problems when investigators raided his office, and he was later stretchered from hospital into court. When no judge could be found on Sunday for a hearing on the tax official’s detention, protesters spent the night outside the courthouse to ensure he did not leave before a judge arrived on Monday morning.

“Inspiring to see Ukrainian civil society in action calling for effective and transparent judicial process,” the US embassy in Kiev tweeted on Sunday night. “The need to establish [an] independent anti-corruption court is clear and growing more urgent,” the embassy added.

Activists’ struggle

Mr Nasirov could be the first senior official to face trial since Ukraine’s revolution three years ago, when anti-corruption protests prompted the country’s then pro-Kremlin leaders to flee to Russia.

The new national anti-corruption bureau (Nabu) that is investigating Mr Nasirov is cited as an example of positive change in Ukraine, but activists still face a constant struggle with officials who block reforms and the fight against graft.

Legal experts say the efforts of Nabu and other prosecutors to bring officials and businessmen to justice are often stymied by an unreformed court system, in which longserving judges are susceptible to bribery and intimidation.

Daria Kaleniuk, executive director of Ukraine’s anti-corruption action centre, said that since Ukraine became independent in 1991 no official with Mr Narisov’s influence and connections had been detained.

“I’m very happy that the first ‘big fish’ is the head of the fiscal service . . . which continues to be the money-laundering machine and resource for dirty cash that is poured into elections,” Ms Kaleniuk told Ukraine’s Hromadske television.

Mr Nasirov was notorious for “attacking and undermining all possible attempts from reformers to change the tax administration and customs service. He was simply protecting a very corrupt, traditional system,” she added.

Activists and reformist deputies have long accused Ukrainian president Petro Poroshenko of protecting Mr Nasirov, and they believe the tax agency boss could provide a wealth of information about the financial misdeeds of the nation’s elite.

Meanwhile, in a case before the International Court of Justice in the Netherlands, Ukraine accused Russia of fuelling terrorism by arming and funding separatists who seized parts of eastern Ukraine in 2014. Moscow rejects the allegations.