(Updates with Shell reaction)
LIBREVILLE, Jan 12 (Reuters) - Royal Dutch Shell workers in Gabon began an "unlimited" strike on Thursday at allthe company's operations in the Central African OPEC membercountry, the workers' union wrote in a letter to employees.
Shell is in advanced talks to sell its Gabon assets, whichone source estimated could be worth $700 million, leavingworkers worried about layoffs or being moved to new locations,the union said.
The national union of petroleum employees (ONEP) said thestrike "will cover all of Shell Gabon's operations (Libreville,Port-Gentil, Gamba Rabi, Koula and Toucan)".
Shell, which produces about 55,000 barrels of oil per day inGabon, confirmed the announcement of the strike but declined tosay if it had had an impact on production. It operates the Gambaexport terminal through which an additional 20,000 barrels fromother producers are also exported.
"Our local management team in Gabon is engaged in mediationwith the Ministry of Labour and the union ONEP relating toimpacts on employees from our advanced negotiations with apotential buyer," a Shell spokesman said.
The union demanded in December that all Shell Gabonemployees be transferred to whichever company takes on Shell'sassets, and that no redundancies were made for economic reasonswithin five years of the deal.
Gabon is Africa's fourth largest oil producer with an outputof around 220,000 barrels per day dominated by international oilmajors Total and Shell. (Reporting by Wilfried Obangome; additional reporting by RonBousso in London; Writing by Edward McAllister; Editing by JoeBavier and Alison Williams)