QUITO, Ecuador (AP) _ Colombian rebels seized a helicopter from an oil field in the Amazon jungle early Thursday, kidnapping six Americans and at least four others and flying them into Colombian territory, military officials said.

The hostages, who also included a Chilean, an Argentine and the two Frenchmen, were taken at gunpoint before dawn in the El Coca region, 150 miles southeast of the capital, Quito, military officials said.

An Ecuadorean military communique said the gunmen, whose faces were covered, claimed to be members of the Revolutionary Armed Forces of Colombia, or FARC, Colombia's largest guerrilla group.

The guerrilla group denied any part in the attack.

The military statement added that the helicopter was detected flying near Ecuador's jungle town of Lago Agrio at 6:25 a.m. before passing over the San Miguel River into Colombian territory.

The exact number of hostages wasn't immediately clear. Though the Ecuadorean military said 10 people were captured, Ecuadorean Vice President Pedro Pinto said nine were seized, including one Ecuadorean.

But the U.S. State Department said at least 10 and as many as 25 people were taken hostage by 15 heavily-armed men.

Despite the rebel denial, Pinto said the FARC had claimed responsibility. He added that the group said the hijacking was in ``reprisal for Plan Colombia,'' an anti-narcotics initiative backed by a $1.3 billion U.S. aid package.

``I can assure you with total security that the FARC has nothing to do with this incident,'' rebel spokesman Carlos Antonio Lozada told The Associated Press by phone. ``It is not the policy of the FARC to carry out military operations outside Colombian borders.''

The rebels, whose field commanders operate with substantial autonomy, have had to backpedal on denials in the past.

Last month, a rebel fighter hijacked a commuter plane and forced it down at a FARC-held southern airport. The group initially denied he belonged to their organization, then later conceded he did.

The U.S. Embassy in Quito said it was working closely with Ecuadorean officials to obtain the victims' release.

In Washington, FBI spokesman Bill Carter said its legal attache in Colombia was in touch with Ecuadorean authorities and had ``offered any FBI assistance needed.''

The oil field is operated by Spanish energy giant Repsol YPF SA. Repsol is the parent company of Houston-based Maxus Energy, which said it was not aware of any of its workers being taken.

Three of the abducted Americans are from Oregon-based Erickson Air Crane Co., the U.S. State Department said.

Two other Americans were drilling rig employees from Helmerich and Payne, an Oklahoma-based drilling company, said Steve Mackey, vice president and general counsel for the Tulsa firm. He declined to identify the two employees.

The Ecuadorean military communique identified the Americans as Dennis Correy, Steve Derry, Jason Wavey, David Bradley, Ron Sanders, and Arnold Arfold. No hometowns were immediately available.

The Associated Press obtained an internal document from foreign oil companies operating in Ecuador calling for stepped-up security measures to protect their operations and employees. For several months the army has been beefing up its presence along the jungle border.

The oil field lies in Ecuador's northern territory bordering Colombia's largest cocaine-producing region.

Rebels and paramilitaries are vying for control of vast coca fields and millions of dollars in ``tax'' proceeds for whichever armed group controls the area.

Government spokesman Alfredo Negrete called the kidnappings ``an isolated act.''