Helicopters dropped crack Colombian troops into a former rebel enclave this morning.
The were no reports of resistance from the 17,000-strong Marxist FRC rebel groups.
About 200 soldiers from the army's Rapid Deployment Force flew at dawn into a former military base just outside the town of San Vicente in a southern enclave the government ceded to FARC rebels in 1998 to encourage peace talks.
President Andres Pastrana declared on Wednesday that negotiations to end Colombia's 38-year war were dead. He said he was retaking area after rebels hijacked a domestic airliner and kidnapped a senator on board.
Some 12,000 government troops are massed on the borders of the 16,000 square-mile enclave that had been off-limits to police, military, and all state institutions for the last three years of fruitless peace negotiations.
Military jets flew dozens of sorties over the enclave yesterday and bombed 13 targets it said included FARC camps and arms, chemical and fuel dumps. There were unconfirmed reports that three people died in the bombing.
Overnight, suspected FARC rebels attacked electricity installations in southern Colombia, leaving many areas without power or telephone services. A gas pipeline near the western city of Medellin was also blown up.
More than 40,000 people have died in the last decade alone of Colombia's bloody war between leftist rebels and the army and far-right paramilitary outlaws.