Sri Lankan officials say suspected Tamil rebels have killed four farmers in the eastern part of the country.

Officials say rebels ambushed the ethnic Sinhalese farmers Thursday in the district of Polonnaruwa. The attack occurred near a jungle area where Tamil rebels have been fighting Sri Lankan troops.

In another incident, Sri Lankan police say they found a powerful, unexploded landmine inside a shop near Colombo, Thursday. Police say the bomb was being hidden for use in a future attack. Five suspects have been arrested and the bomb has been defused.

On Wednesday, Sri Lanka's air force said it destroyed the rebels' naval base in the northeastern district of Mullaithivu.

Tamil rebels denied the attack, saying the warplanes hit an institute that makes prosthetic limbs for landmine victims. They claimed the air strike killed two civilians and wounded several others.