Commercial transit trucks are backed up several kilometers at on the Macedonian side of the border with Bulgaria, the Interior Ministry has said.

Macedonia is now considered an alternative route as the blockade at the Bulgaria-Greece border continues.

Bulgarian authorities earlier made two attempts to talk Greek farmers into lifting the blockade that has been going on for nearly a month and has triggered a "counter-blockade" at all border crossings on the Bulgarian side.

Transport Minister Ivaylo Moskovski, who took part in the talks, and Foreign Minister Daniel Mitov have both described the situation as unacceptable and requiring a response from the EU Commission.

Moskovski told the Bulgarian National Radio on Sunday he had been assured by the Greek Ambassador to Bulgaria, Dimosthenis Stoidis, that Prime Minister Alexis Tsipras would meet Greek farmers sometime between Monday and Wednesday next week.

Earlier reports suggested Tsipras was to talk to protesters on Monday.

Farmers are demanding that the government in Athens ditch its proposal for reforms to pension and taxation laws and have repeatedly said they will not retreat from the border crossings, where they have been severely disrupting traffic over the past weeks, unless the cabinet agrees.

In response, Bulgarian transit truck drivers, who are incurring losses worth millions of BGN according to their trade unions, set up this week "counter-blockades" at all six checkpoints at the common border, insisting that farmers should lift their blockade.

On the Greek side, the protest is affecting the two main border crossings used by a vast part of the haulage vehicles, Kulata-Promachonas and Ilinden-Exochi.

Estimates cited by the Bulgarian National Television suggest only up to a third of the transit trucks waiting (some for nearly a week) in long queues at the main crossings are Bulgarian-plated.