Venezuela's president has accused Colombia of sending soldiers across the border into his country's territory, escalating tensions between the Latin American neighbours.

"We are not talking about a patrol with a few soldiers that strayed over a border," Hugo Chavez said on his weekly television show on Sunday.

 "These troops crossed the Orinoco River in a boat and carried out an incursion into Venezuelan territory ... When our troops got there [the Colombian troops] had already gone away."

Colombia rejected the accusations after the defence ministry consulted with commanders in the border area.

Chavez did not say when the alleged incursion took place, but the accusations followed a dispute between the two neighbours over a plan to lease seven bases in Colombia to the US military.

The issue is expected to be discussed at a short regional summit in Ecuador on Monday, however Alvaro Uribe, the Colombian president, is not expected to attend and several Latin American nations - including Brazil, Peru and Chile - have stated that they consider it a sovereign matter.

'US threat'

Chavez, a vocal critic of US policies in the region, has complained that the US could use the bases to destabilise Venezuela and other leftist nations.

"The threat against us is growing," he said. "I call on the people and the armed forces, let's go, ready for combat!" 

Uribe has said that the deal with the US is vital for tackling drug trafficking in the world's largest producer of cocaine. It is an extension of a existing agreement for military co-operation on the issue.

There are less than 300 US troops in Colombia at present and this would rise to no more than 800 under the agreement, officials have said.

In reaction to the plan, Chavez has halted shipments of subsidised fuel to Colombia, saying Venezuela should not be sending cheap gasoline to an antagonistic neighbour.

"Let them buy it at the real price. How are we going to favour Uribe's government in this manner?" he said.

Chavez also urged companies to buy less from Colombia, with which it shared $7 billion of commerce last year. Venezuela exports oil and chemical products to Colombia in exchange for food and textiles.