Myanmar government forces have launched an offensive against a rebel ethnic minority group just across the border from one of Thailand's northern provinces, a senior Thai army officer said on Monday. Government forces and rebels from the Karenni National Progressive Party (KNPP) have clashed three times in the past week, Thai army spokesman Colonel Acar Tiproch said.About six mortars fired during the attacks landed across the border near the Thai village of Ban Mae Suay Oo, in Mae Hong Son province, 924 kilometers north of Bangkok, he said. They fell in jungle areas and caused no casualties, he said. "The Thai border committee has sent a letter of protest and met local Myanmar authorities urging caution in their operations near the border," he told AFP. Myanmar's shelling of a KNPP base located near the Thai border started last Monday after the rebels attacked an army base and killed eight Myanmar soldiers, border sources said.