OTTAWA -- Prime Minister Stephen Harper says a $15-billion bid by China's state-owned offshore oil company for Canada's Nexen Inc. (TSX:NXY), "raises a range of difficult policy questions" for his government.

But Harper says cautionary signals from the United States about the takeover bid will not be a factor in whether the deal ultimately gets the green light.

Nexen, a Calgary-based oil and gas company, is Canada's 10th biggest revenue generator in the industry and there are widespread concerns about it falling under the control of the Chinese National Offshore Oil Co.

The NDP has finally declared itself formally against the takeover after weeks of calling for a full public airing of the sale.

Harper says his government continues to gather what he calls "information and opinion" about the bid while it wrestles with "difficult and forward-looking issues."

The initial 45-day review period by Industry Canada ends Oct. 12 but the government can extend the review by up to another month before deciding whether the sale is a net benefit to the country.