Croatian prosecutors on Friday charged two people, including a top defence ministry official, for bribes allegedly paid over a multi-million euro contract to overhaul the country's military jets.

The official sought bribes from two foreign firms to "ensure an advantage in obtaining a business deal for the overhaul and procurement of additional MiG-21 fighter planes", anti-graft prosecutors said in a statement.

One of the companies refused to pay the 50,000 euros ($53,000) demanded.

But the prosecutors said the second suspect, a Croatian who represented another foreign company, agreed to pay, and gave the official at least 10,000 euros on two occasions in January and February this year.

A deal, worth 17 million euros according to local media, for the overhaul and procurement of the Russian-made MiG-21s was signed with Ukraine's state-run Ukrspecexport in 2013.

Croatia, which has been a NATO member since 2009, had ordered the overhaul of seven MiGs and purchased five more.

But when the planes were delivered in mid-2015, the new jets had to be grounded because of technical problems.

A probe revealed that the planes purchased in Ukraine were older than their documents showed, raising suspicions about their origins as well as whether the overhaul was conducted at all.