Venezuelan Vice President Nicolas Maduro says security forces have uncovered a plot to assassinate him and the head of the National Assembly, as President Hugo Chavez recovers from cancer surgery in Cuba.
Maduro made the claim at a rally on Wednesday to mark the end of dictatorship in the country 55 years ago, but he said action would be taken shortly.
"For several weeks we've been following groups that have infiltrated the country with the aim of making attempts on the life of [Assembly head] Diosdado Cabello and my own," Maduro told a crowd of red-shirted "Chavista" supporters.
"They will not manage it against either of us... Don't be surprised by actions that are taken in coming hours and coming days. Criminals infiltrating our country can't ask for mercy."
Chavez named Maduro as his preferred successor before he went to Cuba in early December for surgery, his fourth operation in 18 months. Chavez has not been seen nor heard from in public since then.
Venezuela's government says his condition is improving after he suffered multiple complications caused by the surgery.
The government over the years frequently has accused outside extremists with seeking to assassinate Chavez and overthrow the government.
As recently as last month, Venezuela expelled a French national, Frederic Laurent Bouquet, after he finished serving four years in prison for an alleged plot to kill Chavez.
Over his 14 years in power, Chavez has repeatedly accused Venezuela's "traitorous" opposition leaders of plotting to kill
him, but has offered little proof.
The opposition says the allegations of plots are a smokescreen to distract from Venezuela's daily problems such a shortages of staple goods, high inflation and one of the worst crime rates in the world.
"Now Maduro comes with the little story that we want to see an attempt against his life and that of Al Capone," opposition leader Henrique Capriles said on Twitter, referring to Cabello as the Prohibition-era US gangster. "Absolute nonsense!"
Both the opposition and the ruling Socialist Party had originally planned large marches for Wednesday, to mark the day in 1958 when military dictator Marcos Perez Jimenez fled the country amid widespread riots and a coup by rebel soldiers.
That had raised the possibility of supporters clashing in the streets, but the opposition subsequently decided to hold a
meeting instead at a large hall in eastern Caracas.
In the city centre, three separate marches by Chavez supporters converged on the 23 de Enero neighbourhood, which was named after the day Jimenez was toppled from power.