* Sherritt says strike started a week ago

* Says should not affect 2015 output f'cast (Adds processing plant production rate)

TORONTO, March 23 (Reuters) - Diversified Canadian miner Sherritt International said on Monday a strike by employees at its Ambatovy nickel mine in Madagascar had forced the company to curb output there.

The company said the strike had started a week ago and was continuing despite efforts to reach a resolution. The mine is running at a reduced capacity due to the strike, curtailing ore feed to its Toamasina processing plant.

Sherritt said work was continuing at the Toamasina plant and that the strike was not expected to hurt its 2015 production forecast.

The strike at the mine had not prevented the attainment of 54,000 tonnes of nickel production on an annualised basis, or about 90-percent of the capacity of the processing plant, Sherritt and its Japanese partner, Sumitomo Corp, said in statements.

The 90-percent production rate is one of the requirements in achieving financial completion on the project, the companies said, adding that they aimed to fulfil all other conditions by Sept. 30.

Sherritt said it would provide updates on any developments at the mine, adding that it was committed to working with employees and government officials to resolve the dispute quickly.

(Reporting by Euan Rocha; Additional reporting by Yuka Obayashi in Tokyo; Editing by Nick Zieminski)