Protesters say leave Argentina's biggest oil field

* Pan American Energy halted Cerro Dragon output

* Field produces 15 percent of Argentine crude

BUENOS AIRES, June 24 (Reuters) - Energy workers said on Sunday they had lifted a four-day blockade at Argentina's biggest oil field, Cerro Dragon, a protest that prompted Pan American Energy LLC to halt output at the site.

Cerro Dragon lies in the Patagonian province of Chubut and produces about 100,000 barrels of crude per day, or roughly 15 percent of total output in the country. Pan American, or PAE , is controlled by oil major BP.

"We've left the field, Cerro Dragon has been liberated but we remain in a state of alert," union spokesman Guido Dickason said, adding that negotiations continued over their demand for an 11 percent pay rise.�

Pan American halted crude extraction as a security measure after about 500 workers seized some facilities at the field on Thursday to demand higher salaries.

No one could immediately be reached at the company to ask whether production had resumed.

BP owns a 60 percent stake in PAE, while the remaining 40 percent is held by Bridas, which is half-owned in turn by China's CNOOC.