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Australian retail chain Woolworths has surprised the investment community by appointing Grant O'Brien as chief executive, reports the Australian press.

Mr O'Brien, who succeeds Michael Luscombe, will act quickly to defend the company's supermarkets from rival Coles, The Sydney Morning Herald said.

In a statement Mr O'Brien, who has worked for Woolworths for 24 years, most recently as COO of the food and petrol division, said Woolworths' A$44bn supermarket operations would drive earnings growth.

Woolworths faces a renewed onslaught from rival retailer Coles, which has trumped Woolworths' earnings growth over the past year and sparked a price war in January. 

"Supermarkets is still the core of our business and our most important business," Mr O'Brien said. 

This is despite Woolworths' preparing to break into the billion-dollar hardware and home improvement sector this year through a joint venture with the US hardware giant Lowe's. 

Monday's announcement by Woolworths chairman James Strong ends months of speculation about succession plans, The Sydney Morning Herald said.

Investors had tipped supermarkets director Greg Foran for the job. 

Mr Luscombe will retire on September 30 after five years at the helm.