0653 GMT March 21, 2018
The Anti-Corruption Bureau of Ukraine (NABU) did not identify the two officials but said the fraud had cost the budget 149 million hryvnias ($5.6 million / 4.7 million euros at today's exchange rate) in 2016.
The bureau said the arrangement involved an oil purchase contract that was later revised to inflate the original price by 16 percent to benefit the unnamed supplier.
"NABU detectives and special anti-corruption prosecutors have detained two suspected culprits -- a deputy defense minister of Ukraine and the director of the state resource procurement and supply department of the Ukrainian defense ministry," NABU said in a statement.
Ukraine's defense ministry said an investigation into two officials whose titles matched those named by NABU was in progress but provided no other details.
Corruption has long ravaged the crisis-torn former Soviet republic and been a top concern of both Ukraine's foreign partners and global financial support organizations such as the International Monetary Fund (IMF).
But NABU has faced stiff resistance since its launch in December 2015 from institutions such as the general prosecutor's office and the Security Service of Ukraine (SBU).
Analysts view both as controlled by vested interests and incapable of leading independent probes into financial misdeeds.
The IMF is pressing the pro-Western leaders who rose to power after a 2014 revolution that ousted a Russian-backed regime to shore up NABU's efforts by setting up a special anti-corruption court.
They say those indicted by NABU often walk free after paying bail.