SYDNEY, March 26 (Reuters) - Key iron ore and liquefied

natural gas (LNG) ports in Western Australia were closed on

Thursday as a tropical cyclone struck off the coast of the

resources rich Pilbara region, the ports' operator said.

Pilbara Ports said operations at the ports of Ashburton,

Cape Preston West, Dampier and Varanus Island were all shut amid

strong gales and storm force winds caused by Tropical Cyclone

Narelle, a category 3 system.

"The system is forecast to continue intensifying, with the

forecast indicating category 4 by Thursday afternoon," the

operator said in a statement.

The Port of Ashburton is used by Chevron ( CVX ) for exports

from its Wheatstone LNG plant and Mineral Resources for

iron ore exports. Rio Tinto is a major user of the

Dampier port for iron ore and industrial salt exports. Oil and

gas producer Santos operates Varanus Island port.

Port Hedland, the world's largest export point for iron ore,

remains open.