Venezuela says it's sending more troops to its border with Colombia after an attack over the weekend left 3 Venezuelan soldiers dead and 10 wounded.

The big picture: The recent incident highlights the instability in the frontier between the two countries, where Colombian guerrilla groups like the ELN — which Colombia says was responsible for the attack — have long operated. Sebastiana Barraez, a Venezuelan journalist who has reported on the situation for nearly two decades, says Venezuela's socialist government has had a mutually beneficial relationship with the rebel groups dating back to Hugo Chavez's time in office — but things are now getting tense.

• According to Barraez, economic alliances have allowed for the enrichment of Venezuelan military and government officials, and the rebel groups. She says the groups have long done the "dirty work" for the regime, which would get a cut of the revenues from extortion and drug trafficking.
• But the dynamic seems to be changing. The ELN has pushed into Venezuelan territory, including in gold mining areas. That led to a clash over the summer in which a Venezuelan Army lieutenant was killed.
• Gold is of particular importance to Venezuela now as its oil revenues dry up. Marshall Billingslea, the U.S. Treasury’s assistant secretary for terrorist financing, said at a Brookings Institution event last week that the regime is trading gold illegally to gain much-needed cash.

What to watch: Venezuela has not accused the ELN of killing its soldiers, or taken a public position about the group's presence in Venezuelan territory. But the Venezuelan military could still decide to increase the pressure, Barraez says.

Go deeper: Map of where Colombian rebel groups are operating.