"The regime of (President Nicolas) Maduro unleashes brutal repression against my campaign teams," Machado, who polls show would beat the incumbent in a fair race, wrote on X.
"These cowardly actions aim to close Venezuela's path to change and freedom in peace and democracy," she added.
Machado has been barred from public office for 15 years by courts loyal to Maduro on charges of corruption widely dismissed as spurious, and for supporting Western sanctions against the regime.
In the latest assault on her presidential ambitions, Venezuela's attorney general on Wednesday accused her and top aides of involvement in a plot to undermine national stability.
Tarek William Saab announced the arrest of Henry Alviarez and Dignora Hernandez, senior officials in Machado's Vente Venezuela political party, over these "destabilizing actions."
The plan, Saab told reporters, had been to "rally the masses using labor and student unions to incentivize a military wing" to lead an uprising and "generate destabilization in the country."
Seven other Machado aides have been arrested in recent days, and warrants have been issued for several more.
The attorney general did not mention any steps against Machado herself.
"We have revealed a series of conspiracies, threats and actions that have as a common denominator the intention of sowing violence and chaos in the country and threatening the life of the president" as well as "high civil and military authorities," said Saab.
'Help, please!"
Venezuela goes to the polls on July 28 with Maduro seeking reelection after 11 years in office marked by sanctions, economic collapse and accusations of widespread repression.
Machado won an opposition primary with 92 percent of votes cast last October.
But since a Supreme Court ruling upholding her disqualification, she cannot hold public office for 15 years -- nor can the man widely seen as her natural replacement, two-time presidential candidate Henrique Capriles.
Machado, 56, has accused Maduro of violating an agreement, signed by the government and the opposition in Barbados last year to hold a free and fair vote in 2024 with international observers present.
That deal had led the United States to ease sanctions to allow Chevron to resume limited crude extraction in Venezuela -- a decision it is now reconsidering given Machado's continued exclusion from the ballot.
Machado has refused to bow out for now, despite seeming to have little chance of overcoming the hurdles the state has placed in her way.
Official nominations for presidential candidates open on Thursday.
At his press conference, Saab presented a video purportedly depicting a confession from one of Machado's accused co-plotters, Emil Brandt Ulloa, in which he allegedly fingered the US Agency for International Development.
Brandt was arrested on March 9.
Vente Venezuela on X condemned what it described as the "kidnapping" of Alviarez and Hernandez and said the "repression of the regime" was intensifying.
A video did the rounds on social media of police officers forcing Hernandez into a van as she shouts: "Help, please!"
The party's headquarters were shuttered Wednesday.
"Once again, those who seek to stay in power at any cost lash out against those who oppose them," Capriles wrote on X.
