Venezuela's opposition coalition on Thursday called for the Vatican to join an international mediation effort with the government, but said it would not back down on a recall referendum against President Nicolas Maduro.

An effort by former leaders of Spain, Panama and the Dominican Republic to launch dialogue "needs to be broadened," the MUD coalition said in a statement.

"We consider the participation of a representative of the Holy See to be fundamental," alongside that of former Spanish prime minister Jose Luis Rodr�guez Zapatero and former presidents Leonel Fernandez of the Dominican Republic and Mart�n Torrijos of Panama, it said.

If a Vatican official were included, and the recall vote against Maduro guaranteed, MUD said it was ready to enter discussions next Tuesday.

The Venezuelan president, however, has demanded the talks take place "without conditions."

His government has also launched hundreds of complaints over signatures gathered to hold the referendum aimed at ousting him.

Venezuela is suffering a deep recession driven by falling prices for its oil exports. The crisis has prompted food shortages and deadly looting.

The opposition blames the socialist president's economic mismanagement.

Maduro meanwhile regularly accuses business elites of waging an "economic war" against him by hoarding supplies to aggravate the crisis.

Archbishop Diego Padron, chairing an annual conference of Venezuelan bishops, said he was willing to help with the mediation bid.

However he also said Maduro "lacked moral authority to call for dialogue and for peace" because of the government's inability to provide food and medicine for the country's population.

In a sign of Maduro's concern at mounting social unrest, the president on Thursday replaced the head of the National Guard, even as he confirmed his defense minister, Vladimir Padrino Lopez, in his post.