Western Colombia ? The newest battle in Colombia’s drug war is being fought in one of the largest tracts of virgin rainforest in the Americas, an expanse of stunning beauty where crystalline rivers weave around mountains hugged by a blanket of trees.

Harried by eradication campaigns elsewhere, drug gangs have been moving into the remote region, bringing in millions of seedlings for coca — the bush used to make cocaine — to be planted by peasants who are felling patches of trees.

U.S. crop-dusters, which helped wipe out more than a quarter-million acres of coca last year in other parts of Colombia, have begun fumigating the new fields in their costly struggle with traffickers.

An Associated Press team, flew over the region Thursday aboard a helicopter to get a look at the new front in the war.

Stretching as far as the eye can see, the rainforest in Choco state reaches into Panama.

Cocaine producers turned to this rainforest, bordered on the west by the Pacific Ocean and the east by the Andes Mountains, after being hit by extensive coca eradication campaigns in southern, northern and eastern Colombia.

Analysts learned of the encroachment by examining satellite photos, which showed the new coca fields popping up, said Capt. Miguel Tunjano of the Colombian Counternarcotics Police. Operations to crush it were quickly mounted in an effort to prevent a “balloon effect” — where drug production pops up in a new area after being squeezed in another.

A helicopter machine gunner looks over the Garrapatas Canyon in Colombia's western Choco state Thursday. In the newest front in Colombia's drug war, cocaine producers are penetrating one of the largest tracts of virgin rainforest in the Americas.

So far, 3,420 acres of coca have been detected in Choco and 1,075 acres have been sprayed, said Maj. Juan Pablo Guerrero, commander of police counterdrug operations in Choco.

Government troops recently carried out a raid, he said.

“We found 152 seed beds with 10,000 plants in each one,” Guerrero said. “That’s more than 1 million plants.”