The Colombian army said Saturday four FARC rebels were killed and three others wounded in a clash with troops conducting an operation in the central department of Meta.

The army said that among the dead was the head of finances for a FARC unit active in the area.

Colombia has issued arrest warrants for 22 active and retired army officers and two civilians for their alleged involvement in an extrajudicial execution of 18 people, prosecutors said.

Sixteen of the killings occurred in 2007 during a military campaign in the Cesar department, with the victims initially recorded as combatants, they said late on Wednesday.

Venezuela has arrested 32 alleged paramilitaries leading smuggling rings since it closed part of its border with Colombia, a top official said Tuesday.

They were captured after intelligence was gathered on such rings, Diosdado Cabello, the national assembly speaker and the country's de facto number two official after President Nicolas Maduro, told official media.

Colombia's President Juan Manuel Santos visited a tense border city Saturday amid an escalating row with neighboring Venezuela that triggered deportations and the exodus of thousands of Colombians back home.

"I am here to make sure our fellow Colombians get the services they need," Santos said as he began the tour of Cucuta, a far northeastern city of about 700,00 with close business ties to Venezuela and which has been on edge.

The United States on Thursday sanctioned four members of a Colombian rebel group for their alleged role in narcotics trafficking and money laundering in Switzerland.

The sanctions freeze any assets of the four may have under U.S. jurisdiction, and prohibits Americans or U.S. entities from engaging in transactions with them.

Colombia's FARC guerrillas admitted Monday to killing a black community leader in the country's southwest in early August, a crime they had strongly condemned.

After initially rejecting any link to the August 3 shooting of Genaro Garcia, an activist for those forced to flee their homes by Colombia's five-decade guerrilla war, leaders of the Revolutionary Armed Forces of Colombia (FARC) admitted one of their units killed him.

Venezuela's President Nicolas Maduro indefinitely closed his country's border with Colombia and declared a state of emergency in part of the frontier region Friday, following an earlier attack that wounded four people.

Tensions run high along the 2,200-kilometer (1,400-mile) porous border, rife with guerrilla and smuggling activity, and the two countries almost went to war in 2008.

Colombian rebels holding peace talks with the government have extended a unilateral ceasefire, one of their commanders said Thursday.

The commander, Carlos Antonio Lozada, one of the FARC guerrilla group's negotiators at the talks in Havana, did not specify how long the extension would last.

Venezuela's President Nicolas Maduro has ordered part of frontier with Colombia closed after four people were wounded in an overnight attack along the border.

Speaking late Wednesday on state-run VTV television, Maduro said two men on motorcycles had attacked soldiers involved in anti-smuggling operations along the northwestern border with Colombia.

Pope Francis is not planning to meet with Colombia's FARC rebels when he visits Cuba in September, the Vatican said Wednesday.

Representatives of the guerrilla group have been holding peace talks with a Colombian government delegation since November 2012 in a bid to end an insurgency dating back to the 1960s which has cost more than 220,000 lives.