Venezuela's opposition coalition said on Monday that four activists from two of its political parties have been detained in recent days, as tensions rise ahead of a July presidential contest.

Gabriel Gonzalez, Javier Cisneros, Jeancarlos Rivas and Juan Iriarte, of the Popular Will and Vente Venezuela parties were arrested between Friday and Monday by security forces who have accused them of instigating hate and of conspiracy, opposition spokespeople said.

Cisneros was later released on Monday evening, Vente Venezuela said in a message via X.

"We will denounce this new attack by the government in all the relevant international venues. We cannot allow these types of grave violations to continue to be committed," opposition presidential candidate Edmundo Gonzalez said during a live broadcast on social media.

The attorney general's office did not immediately respond to a request for comment.

The detentions of the four activists and a journalist, Luis Lopez, come amid favourable polling for Gonzalez, who was tapped as the opposition candidate after Venezuela's top court upheld a ban on holding public office for its primary winner Maria Corina Machado.

President Nicolas Maduro, who is seeking a third term, was favoured by around 30% in a recent poll, compared to Gonzalez's support of 50%.

Thirty-seven activists have been detained this year, including the four recent cases, Machado, who is actively campaigning for Gonzalez, said alongside him in the broadcast.

Six of Machado's former campaign staffers are currently living at the Argentine embassy, where they have requested asylum in the other South American country.