Venezuela's opposition leader Juan Guaido on Wednesday addressed anti-government protesters, calling on them to stage the the largest march in Venezuela's history.
It comes a day after he asked the military to help him overthrow the Socialist government of President Nicholas Maduro.
Thousands rallied to support him and clashed with police in the streets of Caracas.
But while Guaido has the backing of the United States and most Western countries, the armed forces appear to have stood by Maduro, who has support from Russia, China and Cuba.
And that has frustrated Washington.
White House national security adviser John Bolton on Tuesday said Cuban forces in Venezuela were helping Maduro cling to power.
(SOUNDBITE) (English) WHITE HOUSE NATIONAL SECURITY ADVISER JOHN BOLTON, SAYING (TUESDAY): "This really demonstrates the depths to which the Maduro regime has sunk, that they're using these Cuban-directed thugs to conduct their affairs." U.S. Secretary of State Mike Pompeo on Wednesday blamed Moscow for keeping Maduro in power.
(SOUNDBITE) (English) U.S. SECRETARY OF STATE MIKE POMPEO, SAYING: "There are indications that Maduro was prepared to leave, and that the Russians asked him not to go." Russia on Wednesday denied that allegation.
Maduro has called Guaido an American puppet, and blamed Bolton and Pompeo by name for instigating the unrest.
(SOUNDBITE) (Spanish) PRESIDENT NICOLAS MADURO, SAYING: "Mr. Pompeo, what a lack of sincerity.
Mr. Bolton also gave orders to military and civilian personnel in Venezuela to join the coup.
[FLASH] And Mr Trump set off a thousand expletives, lies.
My God, how far are the men in the United States government willing to go." But we have yet to see how far the U.S. is willing to go, something Pompeo left open.
(SOUNDBITE) (English) U.S. SECRETARY OF STATE MIKE POMPEO, SAYING: "Military action is possible, if that's what's required.
That's what the United States will do.
[FLASH] We'd prefer a peaceful transition of government there." (SOUNDBITE) (English) HOUSE ARMED SERVICES COMMITTEE MEMBER, JIM LANGEVIN (DEMOCRAT-RHODE ISLAND), ASKING: "Have any of you in any way, shape or form been given instruction by your leadership to prepare for any type of military conflict?
A senior Pentagon official on Wednesday told Congress the military had not been instructed to prepare for operations in Venezuela.
(SOUNDBITE) (English) ASSISTANT SECRETARY OF DEFENSE FOR INTERNATIONAL SECURITY AFFAIRS, KATHRYN WHEELBARGER, SAYING: "In this case, we have not been given those sorts of orders that you're discussing.
No." The White House is convening a meeting of the National Security Council on Wednesday.