APURE, VENEZUELA (BLOOMBERG) - Deadly clashes between Venezuelan security forces and illegal armed groups have sent thousands of civilians fleeing over the border into Colombia for safety.

More than 3,100 Venezuelans have crossed the frontier "in a forced manner", since fighting erupted this week, Colombia's Foreign Affairs Ministry said Wednesday (March 24) in a post on Twitter.

The violence, in the Venezuelan border state of Apure, continued on Wednesday, with explosions at a tax agency office there and a National Guard checkpoint, according to the human rights group Fundaredes.

The military fired on the militias from helicopters, according to Fundaredes, while local media reported that a truck belonging to state electric company Corpoelec was attacked.

Venezuela accused Colombia in a statement of supporting the illegal activities of "criminal groups" on the border, including drug trafficking and illegal mining.

President Nicolas Maduro's government said that these armed groups have attacked civilians, electrical and oil installations, and even placed landmines in the area.

Several illegal armed groups operate along stretches of the 2,250km border, and often fight for control of trafficking routes for people and cocaine. Distortions and shortages caused by Venezuela's socialist model often create a lucrative trade in smuggling basic goods in both directions.

As at Monday, at least three people had died in the fighting, Venezuelan Defence Minister Vladimir Padrino said. Two were soldiers, and one was the leader of an illegal group, he said.

The military has destroyed six camps used by the groups, and detained 32 people, Mr Padrino said on Monday.

Marxist guerrillas from Colombia's National Liberation Army, or ELN, and various factions of Farc rebels who rejected the 2016 peace process with their government have a presence on both sides of the border, according to Mr Jeremy McDermott, co-founder of Insight Crime, a think-tank that studies organised crime.

Several other organised crime groups, including the so-called Gulf Clan, also operate in the area, he said.

The authorities do not protect the civilians caught in the middle who have lost "their crops, their cattle and their houses", said Mr Luis Lippa, an opposition lawmaker in Apure, in a phone interview.

Nearly 2 million Venezuelans have moved to Colombia in recent years to escape hunger and chaos back home.