Interstate Power and Light Co. says it plans to seek regulatory approval to build a new natural gas-powered electricity generation plant in Marshalltown. The plant, expected to cost between $650 million and $750 million, won’t become operational before mid-2017.

The announcement was made Thursday by Alliant Energy Corp., Interstate Power’s parent company.

Construction can’t begin until after regulatory approval is granted. The company says that’s expected by the end of 2014.

The plant is one part of the company’s long-term plan to meet electricity demands of its Iowa and Minnesota customers.

Interstate Power also plans to seek regulatory approval purchase electricity from NextEra Energy Resources, which operates the state’s only nuclear power plant.

State regulators are expected to make a decision on that application by early next year.