Restart date unclear for Venezuela refinery hit by blast

* Renewed production following blast still days away

* Process to restart refinery will be "gradual"

* Amuay refinery still cooling after fires

CARACAS, Aug 29 (Reuters) - A restart to production at Venezuela's largest oil refinery, closed since Saturday by the world's deadliest refinery accident in fifteen years, could take another two to three days, officials said, although an exact date was unknown.

Energy Minister Rafael Ramirez said in televised comments on Wednesday that fires at the Amuay refinery, where 48 people died, had been finally extinguished and workers were moving ahead with preparations to restart production.

The "gradual" process could possibly take "two or three days", Ramirez said, although officials at the refinery told Reuters the final timing for a restart could not be determined while parts of the facility continued to cool.

"While the cooling efforts continue, we can't know an exact date," said an official from state oil company PDVSA, which runs the 645,000 barrels per day refinery.

Meantime, authorities will continue to investigate what may have caused the gas leak that led to the blast.

In addition to those killed, the pre-dawn explosion destroyed hundreds of nearby homes. The accident was the most deadly for the global oil industry in recent years, nearing the toll of a 1997 fire at India's Visakhapatnam refinery, which killed 56.

Ahead of presidential elections in October, opponents of President Hugo Chavez have seized upon the blast to criticize what they say is poor upkeep of facilities in the oil industry, the motor of Venezuela's economy. Before Saturday's blast, the country's refineries have routinely suffered lesser accidents and numerous unplanned outages.