Leftist rebels killed at least 25 soldiers in two clashes Saturday in Colombia, the worst death toll in a single day for the military since President Alvaro Uribe came to power three years ago on pledges of crushing the guerrillas. Another 18 soldiers were reported missing. Fighting broke out in southwestern Putumayo state when as many as 300 rebels of the Revolutionary Armed Forces of Colombia, or FARC, ambushed an army convoy during an attack targeting several nearby oil wells, said Gen. Carlos Lemus, Inspector General of the Army. The military responded by sending helicopter gunships to strafe rebel positions while warplanes swooped down to drop bombs, Lemus said. He said the rebels also had suffered casualties but was unable to provide details.Television footage showed villagers scurrying for cover along a dirt road as shots rang out and troops carrying wounded comrades wrapped in blood-soaked bandages on their shoulders. The military reported at least eight injured. Lemus said at least 19 soldiers were killed and he announced a search and rescue operation for 18 soldiers who went missing during the battles near Puerto Asis, 330 miles southwest of Bogota. Putumayo is rich in oil and one of Colombia's main cocaine-producing centers. "We were engaged in very heavy fighting at dawn and called in air support," Lemus said at a news conference. "The attack was directed against petroleum installations."