BOGOTA (Reuters) – Colombia has sent a letter of protest to Venezuela after it said security forces from the socialist country crossed the border into the Colombian province of La Guajira over the weekend, two government sources said on Monday.

The sources told Reuters the Colombian Foreign Ministry had given the letter to Venezuela’s embassy in Bogota, although the government of Venezuelan President Nicolas Maduro denied on Sunday that the crossing into Paraguachon, La Guajira, took place.

The governor of La Guajira criticized the crossing on Twitter over the weekend, saying the security forces came over the border on Saturday night and stole money and cellphones from residents.

Long-standing tensions between the neighboring countries have escalated since Colombian President Juan Manuel Santos joined with other countries in the region to criticize Maduro and said Venezuela was heading toward a dictatorship.

Venezuela’s former top prosecutor, who has accused Maduro of involvement with corruption, fled to Colombia this month.