CARACAS (Reuters) - Venezuelan security forces on Tuesday blocked legislative chief Juan Guaido from entering the congressional palace, after a confused melee on Sunday allowed the ruling Socialist Party to install new parliamentary leadership.

Guaido had pledged to attempt to preside over Tuesday's session anyway. Local television images showed Guaido arguing for several minutes with troops blocking the entrance to the legislative building.

Allies of President Nicolas Maduro swore in Luis Parra as parliament chief on Sunday, seizing the one major state institution that lay outside of Maduro's control.

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.

Local television images on Tuesday morning showed Parra and his allies seated in the leadership posts within the congressional chamber, while a handful of lawmakers allied to Guaido within the chamber screamed at him and referred to the situation as a "coup."

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, soldiers with riot shields blocked Guaido from entering parliament for what was expected to be his re-election. After Parra's swearing-in, Guaido held a separate session elsewhere in which 100 lawmakers backed his bid. The legislature has 167 seats.

Guaido has vowed to preside over Tuesday's legislative session despite what he called Parra's "parliamentary coup."

Parra has rejected that description and said in a post on Twitter: "We came to save parliament from destruction."

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.

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

Tuesday's session, he said, would debate proposals to tackle widespread shortages of gasoline, the freedom of political prisoners, and increases to workers' salaries. The session began around 10 a.m. local time (1400 GMT).

(Reporting by Angus Berwick, Mayela Armas, Vivian Sequera, Corina Pons and Brian Ellsworth; Writing by Luc Cohen; Editing by Brian Ellsworth, Rosalba O'Brien and Bernadette Baum)