"Military deserters have become mercenaries of the Colombian oligarchy and conspire from Colombia to divide the armed forces," Maduro said, without providing further details, as he led a march of 2,500 soldiers at a barracks in Caracas on the same day as a demonstration called by the opposition.

Maduro is in the midst of a standoff with Juan Guaido, the leader of the opposition-held National Assembly who last week declared himself interim president.

Washington threw its weight behind Guaido's claim, having previously termed as fraudulent the May 2018 election that saw Maduro win a second term.

Several European powers meanwhile have given Maduro an ultimatum to hold fresh elections or they too will recognize Guaido.

To keep up the pressure, Guaido has called mass demonstrations against the government this week, and has appealed to the powerful military to change sides, offering amnesty to those who do.

Maduro said Wednesday he would be willing to negotiate with the opposition and hold early congressional elections, in a concession as opponents plan another big demonstration.

But at the same time, he dismissed the possibility of holding a new presidential poll anytime soon.

At least 40 people have been killed in clashes with security forces nationwide and at least 850 arrested since January 21 when a brief military rebellion was put down in Caracas, according to the UN human rights office in Geneva.