CARACAS (Reuters) - Venezuelan security forces let U.S.-backed opposition leader Juan Guaido enter the legislative palace on Tuesday amid a showdown for control of parliament after the ruling socialist party installed its own rival congressional chief.

Guaido, who was re-elected on Sunday to a second one-year term as head of the opposition-held congress, had pledged to preside over Tuesday’s opening session after security forces blocked him from the building over the weekend to allow socialist legislators to swear in their own speaker.

Local television images early Tuesday showed Guaido arguing for half an hour with troops wielding riot shields who again blocked the entrance to the legislative building, but eventually allowed him to push past them.

“This is not a barracks. This is the house of laws,” Guaido told the soldiers blocking his entrance. “The military does not get to decide who can enter the house of laws.”

But inside, a brief session led by Luis Parra - who was sworn in by allies of President Nicolas Maduro as parliament chief Sunday - had already ended, according to Reuters witnesses.

Parra’s swearing in on Sunday gave Maduro sway over the last major state institution that had remained outside his control and appeared to mark a setback to Washington’s efforts to unseat him.

The gambit marked an escalation in Maduro’s crackdown on the opposition, whose key international ally - the Trump administration - has so far been unsuccessful in its year-long attempt to oust Maduro through economic sanctions and diplomatic pressure.

U.S. special envoy for Venezuela Elliott Abrams on Monday said Washington was preparing new sanctions to step up pressure on Caracas. But Maduro’s move suggests he does not expect major consequences from the United States, though the government has steered clear of actions - like arresting Guaido - that could provoke a harsher response.

“We once again handed imperialism a defeat,” socialist party Vice President Diosdado Cabello said on his talk show Monday night.

Parra, who was elected to congress in 2015, had been expelled from the First Justice opposition party in late 2019 due to corruption allegations, which he has denied.

Dozens of countries, including the United States, denounced Parra’s appointment as illegitimate, and said they continued to recognize Guaido as the parliament’s head and as Venezuela’s rightful president.

On Sunday, after soldiers prevented Guaido from entering parliament, he held a separate session elsewhere in which 100 lawmakers backed his bid despite the earlier swearing-in of Parra. The legislature has 167 seats.

‘THE PEOPLE ARE IN CHARGE’

Slideshow ( 11 images )

Guaido had vowed to preside over Tuesday’s legislative session despite what he called Parra’s “parliamentary coup.” Parra has rejected that description, while saying he wants to end confrontations with Maduro’s government. “We came to save parliament from destruction,” he said on Twitter.

After security forces opened the gates to allow him to pass, Guaido stood in the leadership post and sang the Venezuelan national anthem with allies. Electricity swiftly went out in the chamber, and state television - which had broadcast footage of Parra’s session - cut away from the congress.

“In here, the people are in charge,” lawmakers chanted as Guaido entered.

Slideshow ( 11 images )

Guaido was elected head of the congress in January 2019 and invoked Venezuela’s constitution to assume an interim presidency, denouncing Maduro as a usurper who had secured re-election in a 2018 vote widely considered fraudulent.

So far, Maduro has fended off Guaido’s challenge, retaining control of the armed forces and tightening the noose around opposition lawmakers. More than 30 of Guaido’s congressional allies are in hiding, in prison, or in exile.

Guaido has also been losing support as Venezuelans tired with Maduro lose patience with his floundering movement. It remains to be seen whether his defiant response to Maduro’s move could galvanize his supporters, who turned out by the hundreds of thousands to protest Maduro early last year.

Parra’s new policy agenda focuses on reducing conflict with the government. Maduro was quick to celebrate his swearing-in, highlighting a “rebellion” among opposition lawmakers.

Parra said Monday his priority was to set up a new electoral council to preside over free and fair elections.

His brief session included a debate over proposals to tackle widespread shortages of gasoline. The session began around 10 a.m. and ended in under an hour.