Caracas - Pro- and anti-government groups are battling fiercely for public support over a contested plan by President Nicolas Maduro to have a new body elected this month to rewrite the constitution.The opposition, energised by the release from jail of one of its emblematic leaders, Leopoldo Lopez, is leading the charge against the new assembly to be chosen in a July 30 election.On Monday it organised a demonstration in Caracas, during which dozens of protesters and some security force personnel confronting them were injured.On Sunday, the opposition is to hold its own symbolic public vote on whether the new constitutional assembly should be established."This population has decided to continue the fight for liberty," one opposition lawmaker taking part, Freddy Guevara, said. "Sunday will be the biggest act of civil disobedience in Venezuela's history."With Maduro determined to see through the process - which critics view as a way for him to bypass the opposition-led parliament - there are fears of more violence in the streets. Since April 1, more than 90 people have been killed during protests.'Dictatorship'The Venezuelan president, who rules over a once flush oil-rich nation reduced to penury, has been accused by the influential Catholic Church of turning the country into a "military dictatorship."However Russian President Vladimir Putin, a longtime ally, on Monday praised Maduro in a telephone call for "his efforts in maintaining stability and peace in the country," according to a Venezuelan foreign ministry statement.Putin also endorsed Maduro's allegations that he was the victim of a foreign plot to topple him, the statement said.Campaigning for Venezuela's controversial constitutional assembly is to end on July 27.The opposition coalition has said it will not field any candidates in the election it denounces as a "fraud." It has been bolstered by Lopez's exit on Saturday from prison, where he had been kept since 2014 on charges of inciting violence. He is serving the rest of his 14-year sentence under home detention in the capital, although his lawyers said they are looking to have that restriction lifted too, so he is completely free.On Sunday - the 100th day of the protest wave against Maduro - 4 000 demonstrators marched against the president, some of them wearing T-shirts with Lopez's face and carrying banners that read: "One hundred days and I continue to rebel against tyranny.""I reiterate my commitment to fighting until Venezuela's freedom is won," Lopez said in a statement read by a leader of his party. The opposition also said it would continue to press for the liberation of 400 other detainees it describes as "political prisoners," but who the government insists are common criminals.Possible talks?One analyst, Luis Vicente Leon, said switching Lopez from prison to house arrest suggested the government hoped to lower tensions, and that political negotiations now seemed possible. Maduro especially wanted to avoid fractures within the army, without which his grip on power would end, he said.Other observers noted that the opposition leader's release came three days after pro-Maduro militants wielding sticks and pipes stormed the parliament and beat lawmakers, injuring at least seven, during a nine-hour assault. Maduro publicly condemned the violence and said he had ordered an investigation. The officer in charge of parliamentary security was on Monday charged with human rights violations for allowing the attack to happen.Inside Maduro's own camp, there are voices of dissent. The country's attorney general, Luisa Ortega, a strong supporter of Maduro's late predecessor and mentor Hugo Chavez, has come out against the constitutional assembly and criticized government and military actions.Venezuela's Supreme Court is holding legal proceedings against Ortega and is due to rule this week on whether to suspend her from office and put her on trial.A grouping of Latin American and Spanish attorneys general, AIAMP, is to hold an extraordinary meeting in Argentina on Thursday to discuss Ortega's situation. The body has already held two similar gatherings on the same issue. In the most recent one last month, it voiced support for Ortega and slammed the "illegal" pressure against her.