Ukraine recalled two of its diplomats from Poland on Monday after they were accused of trying to smuggle 16 kilograms of gold and 90 000 packets of cigarettes.
Tens of thousands of dollars in cash was also seized from an official embassy vehicle making its way across the border into Poland from Ukraine, Kiev's state bureau of investigations (DBR) said.
Ukraine's foreign minister said an internal investigation had been launched, condemning the alleged crimes of the embassy attache and a driver.
"I will never cover up the scoundrels who think they can use their diplomatic status... for personal illegal enrichment," Dmytro Kuleba said on Facebook.
The pair were allegedly caught trying to smuggle the contraband into Poland at the Yagodyn crossing point, according to DBR.
Some $140 000 (over R2 million) and 67 000 euros (R1.2 million) in cash were also seized from the van, along with the gold and cigarettes.
If found guilty, the diplomats could face a fine of up to 5 000 euros.
Ukraine is one of Europe's poorest nations and the former Soviet republic has long struggled to stamp out corruption.
Transparency International ranked it 117th out of 180 countries on its latest corruption perception index in January.