Iran expressed renewed support for Venezuelan President Nicolas Maduro Wednesday, as the opposition called for a huge May Day protest after armed clashes erupted in the capital Caracas.

Guaido, who is recognised as acting president by more than 50 governments including those of the United States and Brazil, said troops had joined his campaign to oust Maduro, who is backed by China and Russia.

"We believe the constitutional government of Venezuela needs to continue," Iranian Foreign Ninister Mohammad Javad Zarif told reporters on the sidelines of the Asian Cooperation Dialogue in Doha.

"We are happy that the people of Venezuela defeated the coup, but we continue to believe in the need for discussions as the government has suggested.

"We have always encouraged intra-Venezuelan dialogue." The Syrian government, a key ally of Iran, on Wednesday also voiced support for Maduro.

Both Iran and Venzuela have been hit by crippling US sanctions on their key oil sectors.

US sanctions on Venezuela's state oil firm went into effect on Sunday in what Washington hopes will be a major blow in its campaign to topple leftist firebrand Maduro.

Washington reimposed sanctions on Iranian oil exports in November after withdrawing from a landmark 2015 nuclear deal between major powers and Tehran earlier last year.

From Thursday, it ended oil purchases waivers it had granted to Iran's main customers, including China, Russia and Turkey which have all vowed to defy any effort by Washington to impose its writ.

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