Venezuelan opposition leader Juan Guaido is calling more openly than ever for US assistance, as he continues to seek fresh elections in the country.

In a letter posted early Monday, Carlos Vecchio -- Guaido's appointed ambassador to the US -- requested a meeting between the US Southern Command and Guaido's representatives.

For months, the US has refused to rule out military action in support of Guaido's movement. However, US President Donald Trump has also urged caution among senior advisers moving forward, and expressed frustration that some aides were openly hinting at a US military intervention in Venezuela, according to officials familiar with the matter.

Guaido is Venezuela's National Assembly President, recognized as the country's legitimate interim president by more than 50 countries, including the United States. As momentum slows in the nationwide protests that he regularly organizes, Guaido has begun to eye new strategies for political change in the country.

Venezuelan President Nicolas Maduro's administration dismissed the letter, with Vice President Delcy Rodriguez saying during a nationally televised press conference that her council read and rejected Vecchio's request. "Asking for a military intervention in Venezuela" was an attempt to destabilize the country, Rodriguez said.

The letter follows a speech that Guaido gave in Caracas on Saturday, when he echoed Donald Trump's words, saying that "all options are on the table" and argued that a foreign "intervention" had already taken place in Venezuela -- not by the US, but by Cuba, which supports Maduro's government.