(Adds CEO comment, forecast, shares) SYDNEY, Feb 22 (Reuters) -...

(Adds CEO comment, forecast, shares)

SYDNEY, Feb 22 (Reuters) - BlueScope Steel Ltd (BSL), Australia's biggest steelmaker, said first-half net profit more than doubled as a result of it taking full ownership of a steel mill in the United States and due to the impact of a declining Australian dollar.

Net profit was A$200.1 million ($142.8 million) for the six months to Dec. 31, up from A$92.7 million in the previous corresponding period, the company said in a statement on Monday.

The result included a A$702.9 million upward revaluation of the North Star steel mill after BlueScope bought joint venture partner Cargill Inc's [CARG.UL] half share in October, offsetting a A$567.5 million impairment charge due to lower iron ore prices.

Excluding one-off items, the company said underlying net profit rose 47 percent to A$119 million.

Like other Australian steelmakers, BlueScope has had to cope with weak steel prices and lower demand in Asian export markets.

In 2015, it cut 10 percent of its Australian workforce, froze wages and persuaded the New South Wales state government to give it a tax break to keep open its flagship plant at Port Kembla, 60 miles (97 km) south of Sydney.

"Our focus on costs and lifting the performance of steelmaking operations in Australia and New Zealand is paying off," BlueScope Chief Executive Officer Paul O'Malley said in the statement.

He added that the company expected pre-tax earnings in the second half to grow 60 percent, compared to the previous second half.

BlueScope shares touched a one-year intraday high of A$5.71 before easing to trade up 1 percent at A$5.53 by 2358 GMT, while the broader market (xjo) rose about 0.5 percent.

($1 = 1.4010 Australian dollars)