Border agencies were left scratching their heads after expensive equipment was covertly used overnight to “widen and raise the gravel track, and put in more turning and passing points”.

The road, which runs along the Russia-Belarus border, is supposedly a high-traffic thoroughfare for fruit smugglers.

Customs officers recently ambushed nine lorries using the road to transport 175 tonnes of Greek and Polish fruit worth €175,000.

However, they have yet to figure out who was responsible for improving the road - and local authority chiefs have been slapped down by customs officials after joking about writing a letter of thanks to them.

The Smolensk Region Border Agency says it does not have the authority to dig up the road, but now has it on constant surveillance.