BOGOTA — Hundreds of Venezuelan troops moved today toward the border with Colombia, where trade was slowing amid heightening tension over Colombia’s cross-border strike on a rebel base in Ecuador.

The Organization of American States scheduled an emergency afternoon meeting in Washington to try to calm one of the region’s worst political showdowns in years, pitting American-backed Colombia against President Chavez of Venezuela and his allies. Colombian and Ecuadorean officials, meanwhile, traded accusations in the United Nations and the International Criminal Court.

The escalation of tensions was triggered over the weekend when Colombia troops crossed the border with Ecuador and killed a top commander of the Colombian FARC rebels who had set up a camp there, Raul Reyes.

Mr. Chavez, who sympathizes with the leftist rebels, condemned the killing and angrily ordered about 9,000 soldiers — 10 battalions — to Venezuela’s border with Colombia. He warned President Uribe of Colombia that any strike on Venezuelan soil could provoke a South American war.

Colombia’s defense minister said yesterday that he would not be provoked into mobilizing troops in response.

President Bush said America will stand by Colombia and criticized Venezuela’s government for making “provocative maneuvers.” Colombia has received some $5 billion in American aid to fight drugs and leftist rebels since 2000.

A retired Venezuelan general, Alberto Muller Rojas, a former top Chavez aide, said the troops were being sent to the border region as “a preventative measure.”

Soldiers boarded buses and trucks at the Paramaracay base in central Venezuela this morning, and battalions also were moving out from the northern state of Lara, a pro-Chavez governor, Luis Reyes, said.

The Venezuelan military has been tightlipped about troop movements. Venezuela’s armed forces include about 100,000 troops, Mr. Muller Rojas said. Colombia’s American-equipped and trained military has more than twice as many.

Mr. Uribe said his government would ask the International Criminal Court to try Mr. Chavez for “genocide” for allegedly financing the Revolutionary Armed Forces of Colombia or FARC, the country’s main rebel group. He cited a reference to a $300 million Venezuelan payment in documents found in a laptop the Colombians said belonged to Reyes.

The biggest losers from the killing of Reyes appeared to be the hostages that FARC rebels have held for years, pending a swap with rebel prisoners.

Ecuador and France said they had been communicating with Reyes, trying to secure a hostage release, when Colombia’s air force crossed the border to bomb his jungle camp. Along with Reyes, 20 other rebels were killed.

“I’m sorry to tell you that the conversations were pretty advanced to free 12 hostages,” President Correa of Ecuador said in a nationally televised address. “All of this was frustrated by the war-mongering, authoritarian hands” of the Colombian government.

A French Foreign Ministry spokeswoman, Pascale Andreani, confirmed that France was in contact with Reyes as well, and that “the Colombians were aware of it.”

Colombia said documents in Reyes’s laptop indicate that Mr. Correa’s internal security minister met recently with a FARC envoy to discuss deepening relations with Ecuador, and even replacing military officers who might oppose that.

Publicly, there had been no indication of even preliminary progress in securing the release of any of the 40 hostages the FARC wants to swap for hundreds of jailed guerrillas.

Those hostages include three American military contractors and a former Colombian presidential candidate, Ingrid Betancourt, a dual French national who has become a cause célèbre in Europe.

Saturday’s raid followed on the heels of last week’s release by the FARC of four hostages to Venezuela’s justice minister, Ramon Rodriguez Chacin. The minister said the raid proved the “intent of the fascist Colombian government is to hamper the handover of hostages, because that is the path of peace.”

Several Latin American leftist leaders have suggested America was intimately involved in executing the raid that killed Reyes. Colombian military officials have said American satellite intelligence and communications intercepts have been key to putting the FARC on the defensive.

Today, a spokesman for the U.S. Southern Command would neither confirm or deny American military participation. “We do provide intelligence support to partner nations but I can’t get into details on operations,” Jose Ruiz said from Miami.

Another victim of the crisis may be border trade worth $5 billion a year, most of it Colombian exports sorely needed by Venezuelans already suffering milk and meat shortages. Ecuador also depends on some $1.8 billion in trade with Colombia.

Venezuela said it would stop new exports and imports. At one closed border crossing, in Paraguachon, Venezuela, authorities stopped trucks lined up for about a half a mile this morning. But traffic was flowing normally at another crossing, in El Amparo, where a handful of Venezuelan troops stood watch as usual, the customs office was open, and traffic passed freely.

Colombia’s national police chief, General Oscar Naranjo, made a series of shocking allegations based on documents in laptops he said were seized by commandos after the bombing at the camp. Among them, he said, was evidence that Mr. Chavez gave the rebels $300 million for some sort of “armed alliance.”

He said other documents suggest Mr. Correa’s administration was deepening its relations with the rebels, considered a drug-dealing band of terrorists band by the European Union and America.

And the Colombian police chief even said some documents suggested the rebels were seeking to buy uranium, though he gave no details.

Both Venezuela and Ecuador expelled Colombia’s ambassadors in the wake of the attack and dismissed the allegations as lies.

Venezuela later displayed the laptop of a slain drug trafficker, and said it implicates General Naranjo in the cocaine trade.

Mr. Correa flew to Peru today as the first stop in a regional tour to rally other Latin American leaders against Colombia. Other diplomatic efforts to defuse the crisis were under way in Washington today, where an emergency OAS meeting was scheduled.