Fighting sleaze is a priority for Kyiv as it seeks membership of the European Union and tries to strengthen state institutions following Russia's invasion last year.
Oleksandr Klymenko, director of the Specialised Anti-Corruption Prosecutor's Office, told Reuters that most countries Kyiv has asked to extradite suspects in corruption cases have declined to do so.
"In 90% of our cases, we have one or two or three or more subjects who are abroad, and the procedure for handing these people over to Ukraine is complicated," he said during an interview in his Kyiv office.
Countries where suspects have been located included Austria, Spain and Britain, he said.
Easing extradition, Klymenko said, was "extremely relevant" to Ukraine's efforts to root out corruption, which the European Commission, the EU executive, has singled out as a precondition for membership talks to begin.
"The investigation of a criminal case is quite ineffective when we can't return these people to Ukraine from various jurisdictions for the administration of due justice," he said.
Klymenko said countries typically cite security concerns amid Russia's war and the conditions of detention in Ukraine, but that Kyiv always guaranteed the safe custody of suspects under investigation.
In his role, to which he was appointed in July 2022, Klymenko must remain free from political influence - an important concern of Western governments and international donors who want to be sure foreign aid will not fall into the wrong hands.
Klymenko, 36, had previously worked as a detective for the National Anti-Corruption Bureau of Ukraine, another state body fighting graft.
He said the priority for Kyiv's anti-corruption authorities was to root out the complex schemes and illicit networks that have made graft systemic in Ukraine.
The country ranked 116th out of 180 countries in Transparency International's most recent Corruption Perceptions Index, the result of weak state institutions that came under the control of well-connected people after the collapse of the Soviet Union.
Authorities have ramped up their anti-corruption drive since Klymenko's appointment.
Last week, investigators said they had uncovered a plot involving a former head of the State Property Fund that they believe embezzled more than $13 million.
That followed the first indictments on March 15 in a case involving a sprawling scheme that allegedly led to Ukrainian electricity customers overpaying by more than $1 billion between 2016 and 2019.
Klymenko said such elaborate corrupt ploys would continue unless their high-ranking organisers were targeted and the mechanisms exposed.
"If there's no system - in which a subordinate answers to a higher-up, who then answers to the very top - then I think it would be a success not just for us, but for our country in general," he said.