U.S. President Donald Trump speaks during a joint news conference with Brazil's President Jair Bolsonaro in the Rose Garden of the White House in Washington, U.S., March 19, 2019. REUTERS/Kevin Lamarque

WASHINGTON (Reuters) - U.S. President Donald Trump said on Tuesday that his administration had held in reserve what he called “the toughest of sanctions” to try to cut off revenues to Venezuelan President Nicolas Maduro.

“We haven’t done the toughest of sanctions, as you know,” Trump said after discussing the crisis in Venezuela at the White House with Brazilian President Jair Bolsonaro.

Trump in January slapped sanctions on state-owned oil company Petroleos de Venezuela, known as PDVSA, the stiffest economic measure against Maduro to date. The United States is among countries that have recognized opposition leader Juan Guaido as the legitimate head of state.

But Trump’s administration has not yet tried to prevent companies based outside the United States from buying Venezuelan oil, a strategy known as “secondary sanctions.”

The secondary sanctions were part of Washington’s strategy to cut off revenue to Iran, which eventually helped force Tehran to negotiate a nuclear deal with six world powers in 2015.