Machado, elected to Congress in 2010, is frequently pilloried by Chavez supporters as an out-of-touch elitist whose wealthy background makes her incapable of relating to the poor.

Despite her high profile during the protests, many Maduro opponents criticize her as shrill and overly confrontational.

She rose to prominence in 2003 through an organization that helped the opposition gather signatures for what would ultimately be a failed recall referendum in 2004 against the late socialist leader Hugo Chavez.

That group received financing from the United States, in what Chavez call Washington's meddling in the country's affairs.

In one well-known exchange with Chavez in Congress, Machado called on him to halt state takeovers of private businesses, coining the phrase "to expropriate is to steal."

Chavez refused to enter into a debate, dismissing her by saying "an eagle doesn't hunt a fly."

Government critics point out that she signed a 2002 decree that dissolved state institutions during the de facto government that ruled for less than two days during Chavez's ouster.

She won less than 5 percent of the vote in the 2012 opposition primaries to choose a candidate who would face down Chavez in that year's election. Chavez died of cancer a year ago.

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