BBC: Venezuelan President Hugo Chavez has urged voters to approve constitutional changes in a referendum on Sunday.
Addressing tens of thousands of supporters at a rally in Caracas, he also threatened to stop oil supplies to the US if it tried to disrupt the vote.
The reforms include allowing abolishing presidential term limits and ending the autonomy of the Central Bank.
Mr Chavez said the proposed changes would return power to the people, but critics accuse him of a power grab.
Mr Chavez said that his opponents could try to sabotage the vote, with backing from Washington, through violent protests.
He said: "If this [referendum] is used as a pretext to start violence in Venezuela, Energy Minister Rafael Ramirez on Monday will order that oil exports to North America be stopped."
He added that troops had been sent to "protect" the country's oil fields.
Mr Chavez has accused Washington of conspiring to topple his government and possibly backing plots to assassinate him. US officials have called the accusations ridiculous. Chavez urges reform for Venezuela >>>
WATCH BBC VIDEO:
Hugo Chávez rallies supporters
Mark Alexander
