TORONTO (AP) — Canada approved China's biggest overseas energy acquisition, a $15.1 billion takeover by state-owned CNOOC of Canadian oil and gas producer Nexen, but vowed Friday to reject any future foreign takeovers in the oil sands sector by state owned companies.

Prime Minister Stephen Harper said the government would only consider future takeover deals in the oil sands by state-owned companies in exceptional circumstances.

"To be blunt, Canadians have not spent years reducing ownership of sectors of the economy by our own governments only to see them bought and controlled by foreign governments instead," Harper said.

Harper's Conservative government has been studying whether CNOOC's deal and a smaller foreign takeover, Malaysian state-owned oil firm Petronas' $5.2 billion bid for Progress Energy, represent a "net benefit" to the country. The Harper government also approved the Petronas deal on Friday.

Many expected the reviews to shed light on Canada's policy toward foreign takeovers, particularly when the foreign company is owned by the state.

Concerns have been raised that approvals could lead to a flood of deals that put control of Canada's vast energy in foreign hands.