The US accused Venezuela's President Nicolas Maduro on Monday of a dictatorial bid to wipe his opponents off the political map following his latest poll victory, after he announced the main opposition is barred from next year's presidential election.

Maduro's ruling socialists triumphed as expected in mayoral polls Sunday, taking 300 of the country's 335 mayorships after a boycott by the main opposition parties.

But the president insisted that boycott would cost the opposition dearly: "A party that has not participated today and has called for the boycott of the elections cannot participate any more. That is a criterion of the National Constituent Assembly... and I support them."

That removes from the electoral fray key figures such as Henrique Capriles, Leopoldo Lopez and others, and led the United States to say Maduro was seeking to consolidate his "dictatorship."

"Maduro's attempt to ban opposition parties from presidential elections is yet another extreme measure to close the democratic space in #Venezuela & consolidate power in his authoritarian dictatorship," State Department spokeswoman Heather Nauert tweeted.

"A presidential election cannot be legitimate if candidates and parties cannot freely participate," she added in a statement.

The Venezuelan president based his assertion on the rules of the Constituent Assembly, a controversial Maduro-allied special powers legislature whose legitimacy has been widely questioned in the international community.

"If they don't want elections, what are they doing? What's the alternative? (Civil) war?" the president asked.

The main opposition Democratic Unity Roundtable (MUD) coalition has been battered by crushing defeats in regional and municipal polls and in-fighting over how to deal with Maduro, following months of violent protests that failed to unseat him and left 125 people dead.

The main parties in the coalition boycotted the mayoral polls, citing widespread fraud in the regional elections in October, and had set their sights on regrouping for the presidential election.

Now, that avenue appears to have been closed off by Maduro, who prevails in the OPEC-member despite flirting with a default on huge debts, amid a worsening economic and social crisis marked by hyperinflation and chronic shortages of food and medicine.

- Divide and Conquer -

"It's clear that the result of the municipal elections does not reflect the political preferences of the majority of Venezuelans, but it dramatically worsens the opposition's ability to fight and motivate, something that Chavismo will surely know how to take advantage of," said analyst Luis Vicente Leon.

Chavism, the populist left-wing ideology left behind by late president Hugo Chavez, can count on a huge vote-getting apparatus that is largely loyal to Maduro.

"Maduro will insist on a strategy of bringing forward as much as possible the presidential election to prevent the opposition from regrouping," election expert Eugenio Martinez told AFP.

Vice President Tareck El Aissami said late last month that the president would seek a second six-year term, though he himself has not formally declared his candidacy, beyond occasional hints to supporters.

He told his supporters on Sunday to "prepare for great victories in 2018."

The opposition has few choices.

"The only things that remains for them to do is to reorganize to choose a candidate for 2018, but that still looks very complex because there is no agreement between the main leaders," said Martinez.

Leon said the opposition only has "a very short time to restructure and define a strategy."

Its biggest problem, he said, is that "it does not have a leader that can motivate, organize and revive hope."

Yon Goicoechea, who contested a mayoral seat against the will of his party, said the opposition is simply playing into Maduro's hands.

"If we frustrate more people, if we confuse the electorate more, Maduro will win the presidential elections, not because he cheated, but because of our inability to lead the majority with us," he said.

A Venebarometro poll, conducted between October and November, shows the president's popularity rising from 24 percent to more than 31 percent.

Meanwhile, dissatisfaction at the opposition's performance has risen from 46 percent to 65 percent.

On top of the overwhelming mayoral victory, Maduro's party also wrested control of 20 of the country's 23 regional capitals in Sunday's vote.

In a painful reminder for the opposition of the regional election debacle in October, Maduro's candidate also won a re-run of the regional poll in the oil-rich Zulia region, after the original victor -- an opposition governor -- was sacked when he refused to be sworn in before the Constituent Assembly.