CARACAS, Venezuela — Venezuelan President Nicolás Maduro on Monday celebrated the anniversary of his disputed re-election amid a growing humanitarian crisis and political upheaval.

Maduro tweeted that the May 20, 2018, election, was a “victory” for Venezuelans, though the opposition and many countries have derided it as unfair.

In a speech at a government-organized rally, Maduro said he is prepared to face the opposition in legislative elections, though he has made similar challenges in the past while dismissing allegations that his re-election was fixed.

He referred to a recent effort by Norway to mediate between Venezuela’s opposing factions and said he favored dialogue, though critics accuse him of using past negotiations to play for time.

“Why don’t they respond when I make this proposal?” Maduro said of his election offer to the opposition, which is demanding that he step down to make way for a transitional government before elections can be held.

Meanwhile, members of a loyalist assembly assigned by Maduro to write a new constitution decided to extend their work until the end of 2020. The assembly rivals the opposition-controlled congress, headed by Juan Guaidó, that says Maduro has steered Venezuela toward authoritarian rule and ruined the economy.

The United States has imposed sanctions on Venezuela in a bid to unseat Maduro, compounding the problems of the country’s deteriorating oil industry. Maduro says Guaidó is a pawn in a U.S. coup plot.

Also Monday, Carlos Vecchio, a government opponent who the U.S. recognizes as Venezuela’s ambassador, met with Pentagon officials at the request of Guaidó. The U.S. has insisted “all options” are on the table for dealing with Venezuela’s crisis and Guaidó in recent weeks has publicly speculated about the idea of requesting foreign military assistance to help rid Venezuela of Maduro.

Even so, the U.S. says it is focusing on diplomatic and economic pressure on Maduro, and there are no indications of any military buildup.

Maduro’s re-election to a second six-year term lies at the heart of Venezuela’s political standoff, in which Guaidó has sought unsuccessfully to get the military command to support him. The opposition leader’s failed call for a military uprising on April 30 was followed by deadly clashes between police and protesters.

Ahead of Maduro’s 2018 re-election, the main opposition coalition refused to field a candidate, saying there was no possibility of a fair vote. The government had previously stacked the electoral council and judiciary with its supporters, and the opposition’s most combative leaders were banned from participating, imprisoned or exiled.