Ukrainian President Petro Poroshenko on Monday denied any wrongdoing after documents leaked from a Panama law firm showed him holding three offshore accounts that could be used as tax havens.

A year-long worldwide media investigation into a trove of 11.5 million documents found that the former Soviet state's pro-Western leader had registered a company in the British Virgin Islands that he never disclosed in his income forms.

The Ukrainian leader did not deny the accounts' existence but said they in no way broke either his country's or international laws.

"I may be the first top official in Ukraine who treats declaring assets, paying taxes and conflict of interest issues profoundly and seriously, in full compliance with the Ukrainian and international private law," Poroshenko said in a statement issued on Facebook.

Ukraine is engulfed in a months-long political crisis that has paralysed the government and delayed the release of vital Western aid Genya Savilov, AFP/File

"Having become president, I stopped participating in the management of my assets, having delegated this responsibility to the respective consulting and law firms," he added.

The tycoon-turned-president's attempts to distance himself from the scandal come with the war-torn country already engulfed in a months-long political crisis that has paralysed the government and delayed the release of vital Western aid.

None of the three accounts associated with Poroshenko's offshore firm held more than 2,000 euros ($2,270).

But the "Panama Papers" report said they may have been a haven used by the president to avoid paying taxes on his profitable candy empire.

"Poroshenko was busy setting up an offshore tax haven for his business assets as Ukraine was suffering its worst defeat in Russia's war against Ukraine in the summer of 2014," the report said.

"Poroshenko's action might be illegal on two counts: he started a new company while president and he did not report the company on his disclosure statements," it added.

- Impeachment call -

Radical Party leader Oleg Lyashko -- an outspoken populist who holds 21 of the 450 seats in Ukraine's parliament -- said he has "initiated the start of impeachment proceedings" against the president over the revelations.

Lyashko's efforts are unlikely to get very far because Ukraine still lacks a law spelling out how such impeachment hearings may proceed. They could also only begin after the case is studied by the country's constitutional and supreme courts.

Ukraine's prosecutor general's office said it had studied the leaked information and "found no evidence of a crime".

But the accounts' very existence is likely to reflect poorly on Poroshenko's self-proclaimed efforts to erase the east European state's long history of government graft.

Ukraine's 2014 pro-EU revolution was fed in part by deep-rooted frustration with the Russian-backed leadership's alleged use of state funds for self-enrichment and its brazen disregard for the rule of law.

- Chocolate link -

Poroshenko's financial advisers said the accounts were created to help with the president's sale of his Roshen chocolate business -- an asset he had vowed to get rid of when elected in May 2014.

One of Poroshenko's assistants said a transaction made in the British Virgin Islands would help "improve attractiveness of the Roshen group" given the difficult business climate in war-torn Ukraine.

Poroshenko has been dubbed the "chocolate king" for making a fortune through his Roshen empire. The Panama Papers report estimated the president's wealth at $858 million.

But the Kiev office of the Transparency International anti-corruption organisation accused Poroshenko of breaking Ukraine's basic law.

"His creation of businesses while serving as president is a direct violation of the constitution," Transparency International Ukraine said in a statement.

It further accused 50-year-old leader "of breaking anti-corruption standards".