Venezuela's government on Thursday ordered cable television providers to cut the signal of two Colombian networks, a move that critics, including Colombia's leader, called a crackdown on free speech by President Nicolas Maduro.

The country's telecommunications regulator called for RCN and Caracol Television to be taken off the air for broadcasting a message it said incited Maduro's murder, the office of Venezuela's presidency said in a statement.

"The measure is within the bounds of the law, given that those stations over several months attacked Venezuela and (its) institutionality and now are openly calling for a magnicide," the statement said, citing Andres Mendez, former head of telecom regulator Conatel.

The statement said the message in question was a comment by former Mexican President Vicente Fox, who said: "Maduro, resign or you will die."

The decision was lambasted by Venezuelan opposition political leaders and Colombian President Juan Manuel Santos, who called it another sign that Venezuela was descending into dictatorship.

Caracol, which earlier announced its removal from Venezuelan cable networks, blasted Maduro for engaging in censorship.

RCN said on its evening news broadcast that it categorically rejected the action and that its signal had been cut off at 5:30 p.m. (2230 GMT).

Maduro often criticizes neighbouring Colombia for being part of a right-wing conspiracy to bring down socialism in oil-rich Venezuela. He says Venezuela is the victim of an "economic war" led by adversaries with the help of Washington.

Critics say Venezuela's ruling Socialist Party, which this year led a campaign to create an all-powerful legislative superbody, is seeking to limit coverage of rampant inflation, product shortages and a crackdown on opposition politicians.

"One more channel off the airwaves! Has that made crime go down? Is inflation any lower? Is there more food? More medicine? Has any problem been solved?" opposition leader Henrique Capriles said on Thursday.

Maduro alleges he is fighting well-financed coup plotters with links to the United States and hostile foreign media.

"It's another demonstration of a regime that doesn't like freedoms, a regime that is restricting the freedoms of citizens," Colombia's Santos told journalists.

Earlier this year, Conatel suspended three television channels, including CNN's Spanish-language service, from the airwaves, accusing them of distorting the truth in their coverage.

Authorities took Colombia's NTN24 TV network off the air in 2014 over its reporting of opposition protests that turned violent, and blocked the Argentine news site Infobae.