Key Venezuelan opposition figure Freddy Guevara, arrested for "treason" and "terrorism" last month, was released Sunday -- days after the start of new talks between the opposition and government.

Guevara, 35, was pulled from his car in Caracas by members of the Bolivarian National Intelligence Service (Sebin) and detained on July 12.

Attorney General Tarek Saab charged Guevara with "crimes of terrorism, attacks against the constitutional order, conspiracy to commit a crime and treason," over alleged links to violent clashes earlier in July in a Caracas neighbourhood, which the government of President Nicolas Maduro said were part of a plot to unseat him.

Guevara's release comes as the government and opposition launched new negotiations -- mediated by Norway and hosted in Mexico -- to try to end a crippling political and economic crisis in the country, in which the release of political prisoners is also on the agenda.

The United States had urged Venezuela to free Guevara, a former student leader and lawmaker, saying his arrest cast a shadow over leftist leader Maduro's stated openness to talk with the opposition.

In response to media reports he would join the opposition team at the negotiations in Mexico after his release, Guevara said he did not know if he would take part.

He told reporters on Sunday he was "not clear on what the limitations are" of his release.

One of his lawyers, Teresly Malave, told AFP the judge "has not imposed terms" of his release yet, but that he believed Guevara would be granted full release or have some reporting requirements. He ruled out the possibility of house arrest.

Guevara, elected to parliament in the 2015 vote that gave the opposition control of the assembly under the leadership of Juan Guaido, has been accused in the past by the socialist government of encouraging violence in protests that called for Maduro's departure.