(CNN) -- President Hugo Chavez arrived at the Amuay oil refinery in northwestern Venezuelan on Sunday, one day after an explosion there killed at least 41 people.
Speaking to reporters, he said it was too early to speculate what could have caused the blast, which left more than 80 people injured.
"There was a leak. The gas formed a cloud and it exploded. We must investigate why," said Chavez.
The president has declared three days of mourning.
He said officials have begun a preliminary investigation, but as of yet have been unable to access the exact spot where the explosion occurred.
The early Saturday morning blast damaged refinery infrastructure and ripped through nearby houses.
Among the dead were 18 members of the national guard and 15 civilians, according to Vice President Elias Jaua, state-run VTV reported. Six of the bodies have not been identified. The toll rose to 41 Sunday when two people died in the hospital. The victims had burns covering 100% of their bodies, said Jesus Valdes, health coordinator at Coromoto hospital.
In total, 209 homes and 11 businesses were damaged, Jaua said.
The refinery -- one of the world's largest -- is part of the giant Paraguana complex in Falcon state.
Venezuela, a founding member of the Organization of the Petroleum Exporting Countries, is one of the world's largest oil exporters.
The nation has a refinery capacity of more than 1 million barrels per day, according to OPEC.
The organization said Venezuela's oil revenues represent some 94% of the country's export earnings, more than half of federal budget revenues and some 30% of gross domestic product.
The South American country ships a large percentage of its exports to the United States.