Maduro, a 61-year-old former union leader, was proclaimed as the Socialist party's candidate by Vice President Diosdado Cabello, and took the stage at a large sports arena to address supporters.

"There's just one outcome, the people's victory on July 28," Maduro said, wearing a bright red zippered jacket. "They haven't been able to stop us, nor will they be able to."

Recent polls show 13.9% of Venezuelans plan to vote for Maduro, far behind opposition candidate Maria Corina Machado's 54.5%.

But though Machado won an opposition primary in October, it was unclear whether she will appear on the ballot after the country's top court upheld a ban barring her from holding public office.

Candidates have until March 25 to register and it remained unclear whether the opposition will name a replacement for Machado, who is under increasing pressure to pick a substitute.

The U.S. partially rolled back sanctions on Venezuela's government in late 2023 because of an elections deal with the opposition, but the nascent rapprochement came to an end with arrests of opposition figures and the court decision about Machado. The U.S. has pledged a reinstatement of oil sanctions from mid-April.

Ruling party sources have told Reuters the reversal in policy by Maduro may be due to waning popularity with his base.

Venezuela has suffered hyperinflation and an unprecedented economic collapse since Maduro took power in 2013, after the death of his mentor, President Hugo Chavez.

The country has seen intermittent waves of protest against the ruling party and Maduro, particularly between 2014 and 2017, resulting in dozens of arrests and killings.

The main opposition parties boycotted the 2018 presidential election and refused, along with the U.S. and others, to recognize Maduro's victory.

Maduro squeaked to a 1.5% victory in 2013 elections, which the then-opposition candidate also declared fraudulent.