The EU anti-fraud office OLAF said Friday it uncovered "serious irregularities" in public lighting projects in Hungary reportedly involving a firm once part-owned by Prime Minister Viktor Orban's son-in-law.
Opponents of the right-wing Orban, expected to win a third consecutive term in elections in April, have long accused him of presiding over a corrupt system that enriches his close associates.
"OLAF's investigation revealed not only serious irregularities in most of the projects, but also conflict of interest", it said, noting the probe was complete.
The OLAF investigation concerns contracts worth tens of millions of euros (dollars), part funded by the European Union, to modernise street lighting won by the Elios company between 2011 and 2015, the Wall Street Journal reported.
At the time Elios was part-owned by Istvan Tiborcz, who is married to Orban's daughter, and a second man who also owned another company that advised local authorities on public tenders -- hence the possible conflict of interest.
OLAF said it has sent its final report to the European Commission, and judicial recommendations to the public prosecutor's office in Hungary.
Hungarian authorities already launched an investigation in 2015 but it was dropped a year later.
Tiborcz, whose considerable directly and indirectly owned real estate assets include a number of castles and hotels, according to local media reports, sold his stake in Elios in 2015.
Neither Tiborcz nor Elios could be reached for comment.
A spokesman for the Hungarian government said Friday that Budapest was in favour of a new investigation, saying the contracts in question were awarded under the previous left-wing government.