Prime Minister Stephen Harper says the national-security angle to Canada's relationship with China is something his government takes very seriously.

The remarks Friday came amid renewed concerns about Chinese espionage and also as Harper faces a major decision on an oil-industry takeover by a state-owned Chinese company.

Harper said he couldn't comment on specific transactions but noted that the relationship with China is complex because the world giant has different political and economic systems.

''The relationship with China is important. At the same time it's complex," Harper told a news conference. "It's complex because the Chinese have obviously very different systems than we do — economic and political systems. . .

''Of course, as you know, there's a national-security dimension to this relationship, in fact to all of our activities, that we take very seriously.''

The prime minister was speaking at a news conference in Senegal shortly before leaving for la Francophonie summit in the Democratic Republic of the Congo.

The comments came a day after his government extended its review period for the proposed takeover of Calgary-based Nexen Inc. (TSX:NXY) by China's state-owned offshore oil company.

The NDP has called on Ottawa to block the $15.1-billion takeover and has cited various concerns, including national security.

Concerns about commercial dealings with China were heightened this week by a U.S. congressional report that two of its leading high-tech companies are a threat to national security and flout foreign laws. One of the companies mentioned in the report, Huawei Technologies Ltd., is active in Canada.

Harper was asked at Friday's news conference about the U.S. House Intelligence Committee report, in the contect of the Nexen takeover.

"Obviously, some of these particular transactions raise concerns,'' Harper replied.

"We will ensure as a government that we have not only a growing relationship with China but a relationship with China that is in Canada's best interersts — that always serves the broader interests of the Canadian economy."

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