Farmers armed with machine guns,rocket-propelled grenades and mortars forced government troops to abandon an operation to destroy their illegal cannabis crop in Lebanon's Bekaa Valley on Monday, a witness said.

No casualties were reported in the exchange of fire but two security force vehicles were hit by bullets, the witness said.

During Lebanon's civil war, which took place between 1975 and 1990, the fertile Bekaa Valley produced up to 1,000 tons of cannabis resin annually and 30 to 50 tons of opium, used to make heroin.

The crop was eradicated by a United Nations program put in place between 1991 and 1993 but it has reemerged as the security forces struggle to control the volatile country. There are no reliable statistics on how much cannabis is produced in Lebanon now.

Security forces run annual operations to destroy marijuana crops but face resistance from angry farmers who see the lucrative and easy-to-grow crop as a way to make money for their impoverished communities.

A security source said government forces were regrouping and planning a new operation to destroy the crop.