Athens - Truck drivers clashed with farmers along the Greek-Bulgarian border Thursday as farmers continued roadblocks across Greece for the fourth straight day to protest falling commodity prices and to demand increased farm subsidies and pensions.

Tens of hundreds of tractors continued to block the Athens-Thessaloniki national highway at the Pembi intersection in central Greece as well as the Mikrothebes intersection in Larissa and Kastro, causing traffic chaos for thousands of motorists.

Blockades also continued at the two northern border crossings of Promachonas in Serres, northern Greece and the Exochi in Drama along the Greek-Bulgarian border.

The blockades caused several kilometres of traffic jams from the large number of trucks that had been prevented from leaving the country and there were many reports of protesting farmers clashing with truck drivers.

The worst clashes were at the Promachona border crossing where trapped truck drivers drove toward parked tractors in a bid to force them out of the way.

Tractors were also deployed along the highway which connects the cities of Hania and Irakleio on the southern Mediterranean island of Crete.

Greek Prime Minister Costas Karamanlis has instructed his ministers to intensify negotiations with the farmers protesting falling commodity prices and demanding higher subsidies and pension payments as well as lower fuel taxes.

Producers say they are particularly upset about the plummeting prices of cotton, corn and wheat, which are set by the European Union and claim that they are struggling to make a living.

Local farmers' unions are due to hold meetings later on Thursday to decide on the further course of the mobilisations. (dpa)