A top legislator in Canada's ruling Conservative Party on Tuesday made public his fierce opposition to a bid by China's CNOOC Ltd for Nexen Inc , underlining the political challenges facing Ottawa as it studies the takeover.

The comments from James Bezan, chair of the House of Commons national defense committee, were among the harshest attacks any Conservative has launched on the landmark $15.1 billion bid.

The government last week extended the review period until Dec. 10 amid widespread unhappiness among Conservatives about the idea of selling a Canadian energy firm to a Chinese state-owned enterprise. Many in the party also have cited China's human rights record as a reason to be cautious.

Although Prime Minister Stephen Harper is keen to sell oil to China and attract more foreign investment, he must also address increasing domestic unease about the deal.

iPolitics, a website reporting on Canadian politics, on Monday said Bezan had criticized the CNOOC bid in an e-mail to a constituent.

"I am strongly opposed to this deal, and I have raised my concerns directly with Cabinet as well as with the Prime Minister ... due to China's dismal record on human rights and freedoms, I take particular exception to allowing a state-owned company from China to purchase a Canadian company," he said.

"The Communist Chinese government continues to fail to grant even the most basic of human freedoms to its citizens, as they strip away their national wealth to invest around the world. CNOOC's past possible human rights abuses and failure to report oil spills is something I am also very concerned about."

Industry Minister Christian Paradis is responsible for studying the bid to see if it is of net benefit to Canada.

Bezan sent an email to Reuters on Tuesday confirming that he had sent the email to the constituent.

"I stand by my comments on the CNOOC purchase of Nexen and have expressed my concerns to Minister Paradis," he said in his email to Reuters.

Harper has said that when the government releases its decision on the CNOOC bid it will also unveil new guidelines for foreign investment, in particular takeover bids by state-owned enterprises.

Ottawa shocked markets on Oct. 5 when it unexpectedly blocked Malaysia's Petronas from buying Canada's Progress Energy Resources Corp.

Canada, the single largest exporter of energy to the United States, says it needs C$650 billion ($657 billion) in investment in the energy patch over the next 10 years alone and concedes much of the money will have to come from abroad.