Venezuela has accused 60 Colombian troops of entering just inside its territory in what it said was a provocation by a warmongering government seeking to destabilize the region.
In an incident likely to stoke already high tensions between the two South American neighbours, Venezuela said the soldiers were intercepted 500 yards (800 metres) over the border and immediately made to return to the Colombian side.
Colombian president Alvaro Uribe, a Washington ally who has received billions in US aid to counter a guerrilla conflict, said he asked defence officials to investigate the accusation.
"If it is true our troops entered in there, then we will offer our apologies. If it is not, we will give our explanation," Uribe told reporters at a news conference. "All we want is to have good relations with our neighbours."
The alleged incursion occurred on Friday, a day after President Hugo Chavez vowed to review diplomatic and trade ties following an Interpol investigation that helped reinforce Colombian charges he supports Marxist guerrillas in Colombia.
Ties in the region have frayed since Colombia raided inside Venezuela's leftist ally and fellow Opec member Ecuador and killed a rebel leader in March. Ecuador broke off relations and Chavez ordered tanks to the sparsely populated border that snakes through jungle and mountains.
"Venezuela views with concern that this act of provocation comes at a time when our government has denounced the belligerent policy of the Colombian government that is deliberately looking to destabilize the region," the foreign ministry said in a protest note distributed to the media.
For years, it has been thought troops and rebels from both sides occasionally strayed across remote parts of the border. But diplomatic protests are rare and yesterday's was the first such complaint since Colombia's raid into Ecuador.