Venezuelan opposition leader Juan Guaido told his supporters Saturday at a rally in Caracas that he had instructed his ambassador to the U.S. to contact the U.S. military to pressure President Nicolas Maduro to step down from his post.

Guaido spoke to demonstrating crowds in the Alfredo Sadel Plaza in Las Mercedes, a commercial district in Caracas.

He spoke a day after a Venezuelan court ordered Edgar Zambrano, vice president of Guaido's opposition-controlled National Assembly, to be held at a military facility. Zambrano,who was arrested earlier in the week, and nine other opposition leaders are under investigation in connection with a failed military insurrection.

U.S. Secretary of State Mike Pompeo has called for Zambrano's immediate release, saying his arrest "is an attack on the independence of the nation's democratically elected legislative branch."

Shippers sanctioned

Meanwhile, the United States has placed sanctions on two shipping companies for transporting Venezuelan oil to Cuba.

The U.S. Treasury Department said Friday that it had targeted Marshall Islands-based Monsoon Navigation Corp. and Serenity Maritime Ltd., headquartered in Liberia.

The agency said the companies owned ships that were involved in oil transfers to Cuba, which the U.S. has accused of providing military support to Maduro.

The Treasury Department said the vessels delivered oil to Cuba from late 2018 through March.

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The U.S. and some 50 other countries support Guaido, who declared himself interim president in January on the claim that Maduro's 2018 re-election was illegitimate.

Maduro has called Guaido a puppet of the U.S. Maduro has held on to power with the support of Cuba, Russia and China. (VOA)