Venezuela's President Nicolas Maduro has said the number of deaths which can be connected to two weeks of anti-government protests has risen above 50.
Official estimates put the number killed in clashes at 13. Mr Maduro has blamed the violence on fascist groups.
He was speaking ahead of a meeting intended to put an end to the unrest, sparked by anger at high inflation, rampant crime and food shortages.
But the main opposition coalition has refused to attend, calling it a farce.
"We will not lend ourselves to a sham dialogue that would end in a mockery of our compatriots," the opposition MUD said in a letter to Vice President Jorge Arreaza.
On Monday, Venezuela's Attorney General Luisa Ortega said 13 people had died in protest-related violence. At the time, opposition groups said the number of dead was at least 15.
Speaking at a pro-government rally staged by farmers outside the presidential palace, Mr Maduro said there were "more than 50 dead as a result of road blocks and barricades".
"Yesterday, an 84-year-old lady died in eastern Caracas because she was held up at a road block for three hours and died in her family's car of a heart attack," he said.
He did not further clarify his reasons for giving a steep increase in the death toll.
Elsewhere in Caracas, hundreds of people, mostly women, led by the wife of imprisoned opposition leader Leopoldo Lopez protested against the government's handling of the demonstrations.
The "national peace conference" was called by President Maduro a few days ago, after another violent weekend.
The Roman Catholic church and a major business federation had confirmed their presence.
The protests have continued, although their numbers seem to be declining.
The leader of the opposition, Henrique Capriles, dismissed the talks initiative as a "photo opportunity" for Mr Maduro.
"Who does dialogue suit more? Nicolas [Maduro], I think. This is a government that is becoming extinct, eating itself up," Mr Capriles told Reuters news agency.
On Tuesday, the UN Secretary-General, Ban Ki-moon, said he was "saddened by the violence" and called for the "protection of human rights" in Venezuela.
Pope Francis also said he hoped that "violence and hostility would cease as soon as possible".
He called on the Venezuelan people "to promote reconciliation through mutual forgiveness and sincere dialogue".
Earlier, US Secretary of State John Kerry said his country was willing to change its tense relationship with Venezuela.
"But we are not going to sit around and be blamed for things we have never done," Mr Kerry said.
The United States has expelled three Venezuelan diplomats, in response to the expulsion of three of its own consular officials from Caracas.
More than a week ago, Venezuela had accused the expelled Americans of having links with violent groups.
President Maduro has been following the example of his predecessor and mentor, the late Hugo Chavez, and accuses the Americans of being behind many of the problems in Venezuela.
The current unrest started two weeks ago with student protests in the western states of Tachira and Merida demanding increased security.
They also complained about record inflation and shortages of staple items.
But it soon spread to the capital and other parts of the country.