Venezuela blocks Colombia border after killings

* Soldiers stop people using main crossing.

* Two Venezuelan soldiers shot dead.

* Chavez government blames Colombian paramilitaries (Recasts; updates throughout; adds byline; changes dateline)

By Jorge Silva

SAN ANTONIO, Venezuela, Nov 3 (Reuters) - Venezuelan soldiers blocked the main border crossing with Colombia on Tuesday after President Hugo Chavez's government said paramilitaries were behind the killing of two soldiers.

In the latest violence in an often lawless region between the Andean neighbors, a gang of four men on motorbikes ambushed and shot dead the Venezuelan soldiers at a checkpoint in western Tachira state on Monday.

Venezuela blamed Colombian paramilitaries for the murders, ratcheting up the diplomatic feud between Chavez's leftist government and the administration of Colombian President Alvaro Uribe, who is Washington's main ally in the region.

"Sadly, our two men were brutally murdered by groups operating in the frontier zone, trying to spread fear and create an atmosphere of insecurity," local army head Franklin Marquez said. The pair were shot in the back in apparent revenge for a crackdown by security forces, he added.

Paramilitary gangs, originally set up to fight Colombian guerrillas, operate in the border area, as do rebels, and a host of criminal gangs trafficking gasoline and drugs.

Witnesses in the Venezuelan border town of San Antonio said dozens of soldiers with an armoured car and machine gun had taken over the road to the nearest Colombian locality, Cucuta.

While large queues of cars formed on both sides, hundreds of locals crossed by foot under a bridge, loaded with suitcases and bags of goods, Reuters witnesses said.

Visiting Tachira, Venezuelan Vice President Ramon Carrizalez said there was no formal closure of the border, but "we are obliged to take strict control measures."

Venezuelan authorities said one man had been arrested for Monday's incident.

The killing of the soldiers was the latest in a string of incidents on the border, including arrests on both sides, and the discovery of 10 corpses of men whom Venezuela said were mainly Colombian paramilitaries.

In a major political spat, Caracas is holding three men -- two Colombians and one Venezuelan -- charged with spying for Bogota. Chavez, who says Colombia has sold out to the United States, cut ties and reduced trade earlier this year.

Colombia's Foreign Minister Jaime Bermudez said his government was ready to talk with Venezuela to reduce tensions. "The door is open," he said during a visit to Ecuador.

"We know there are sensitive issues with that country, but we we want to have the best relations." (Additional reporting by Alexandra Valencia in Quito; Luis Jaime Acosta in Bogota; Eyanir Chinea in Caracas; Writing by Andrew Cawthorne; Editing by Cynthia Osterman)