(Recasts, updates with Calderon comments)

MEXICO CITY, Aug 21 (Reuters) - Mexico will lose 2.6 million barrels per day of its crude oil output until Friday because of Hurricane Dean but state oil company Pemex said it was too early to decide whether to declare force majeure,

The storm, which was a monstrous Category 5 when it slammed into the Yucatan Peninsula on Tuesday morning, forced Pemex to shut down about 80 percent of its crude output and close its three major oil ports.

"This has an economic cost. Mexico will stop producing about 2.6 million barrels of oil per day until Friday," President Felipe Calderon told a news conference on a visit to Canada on Tuesday.

Pemex said it must evaluate damages after the hurricane passes before deciding whether to declare force majeure.

"A decision still cannot be made on declaring force majeure," Pemex spokeswoman Martha Avelar told Reuters.

Mexico has suspended crude shipments from its three major oil ports as the storm, downgraded to a Category 2, approaches the country's main oil producing region in the Gulf of Mexico.

A source at Pemex said it was unclear when the ports will reopen.

The three ports -- Dos Bocas, Cayo Arcas and Coatzacoalcos -- ship the bulk of Mexico's crude exports, which are mostly to the United States.

After killing 11 people on its rampage through the Caribbean, Dean tore into Mexico, landing around the cruise ship port of Costa Maya, near the border with Belize.

Dean was expected to remain at hurricane strength when it passes into the oil-producing Gulf of Mexico on Tuesday evening.

Pemex has closed and evacuated all its 407 oil and gas wells in the Campeche Sound due to Hurricane Dean, slashing its crude output by 2.65 million barrels per day.

That is equivalent to just over 80 percent of Pemex's total daily crude output, which in June averaged 3.2 million bpd. The closure includes Pemex's huge but dwindling Cantarell oil field.

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