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SOFIA (Reuters) - Bulgarian truckers staged a counter-blockade on Tuesday at a checkpoint on the country’s border with Greece, after Greek protesters failed to keep a promise to lift their own blockade for a few hours a day.

“The situation is unbearable,” Mirolyub Stolarski, the head of the Bulgarian association of road transport unions, told Reuters. “What happens is humiliating, people cannot stand this anymore.”

Greek farmers have been intermittently blocking roads into Bulgaria and motorways across Greece for about four weeks, protesting pension reforms that will triple their social security contributions over the next four years.

“Obviously, we have to close the borders and show that there is no border between Bulgaria and Greece,” Stolarski said. “And when they see that their blockade is not important, then they may realize that this is not the way to tie Bulgarian road carriers or Bulgarian citizens’ hands ...”

The Kulata crossing has been closed for all vehicles, causing a 12-km (seven-mile) traffic jam of heavy-fright trucks. The remaining checkpoints at the Bulgarian-Greek border will be closed on Wednesday.

The Bulgarian truckers are demanding that the Greek farmers promise not to block the border any more. According to an agreement reached last week, blockades were to be lifted at certain hours each day to keep vehicles from queuing up.

Last Tuesday, four Bulgarian truck drivers smashed through barriers set up by Greek truckers along the border, saying they were fed up with the Greek protesters barricading roads.

“They said that their families were starving, but what about the families of the people blocked at the border, are not their families starving, too,” Stolarski said.

Bulgarian authorities have called on the European Commission to impose sanctions against Greece, saying the blockades staged by Greek farmers are violating EU principles on the free movement of people and goods.