BOGOTA (Reuters) – A Venezuelan military helicopter flew across the border into Colombia and close to an army base on Wednesday, Colombia said, raising tensions in a months-long diplomatic dispute that has choked off bi-lateral trade.

Venezuelan President Hugo Chavez in November told his army to prepare for war, warning that a military pact signed between Colombia and the United States a month earlier could set the stage for the invasion of his oil-rich country.

Washington and Bogota dismiss the claim, but analysts say there is an increased risk of cross-border skirmishes.

“This morning a Venezuelan military helicopter flew over an army brigade located in the city of Arauca,” Colombia’s foreign ministry said in a statement, which called the incursion “unacceptable.”

The ministry will send a letter of complaint to Caracas asking for an explanation.

Washington says the military deal signed with its ally President Alvaro Uribe is designed to fight cocaine trafficking and insurgents within Colombia and poses no threat to the region. The security agreement gives the US military access to seven Colombian bases.

The breakdown in bi-lateral trade, after leftist revolutionary Chavez halted Colombian imports, has slowed Colombia’s economic recovery and contributed to Venezuela’s already high inflation rate by reducing the supply of goods.