UPDATE 1-Canada opposition party urges CNOOC's Nexen bid be rejected

* Cites lack of transparency in approval process

* Says deal raises alarming number of unanswered questions

* Investment can't be made at cost of sustainable development

(Adds details)

OTTAWA, Oct 4 (Reuters) - The Canadian government must reject CNOOC Ltd's $15.1 billion bid for oil producer Nexen Inc as the Chinese state-owned oil company's offer is currently structured, the main opposition New Democratic Party (NDP) said on Thursday.

"The lack of transparency in the approval process and an alarming number of unanswered questions, have pushed the NDP to reject, as currently structured, the transaction that would allow the state-owned CNOOC to take over the Canadian company Nexen," the left-leaning party said in a statement.

The NDP cannot force the hand of the Conservative government, which has a majority in Parliament, but Prime Minister Stephen Harper has said he will take public opinion into account as his government decides whether to approve the bid.

The NDP statement said the transaction raises many questions, including whether or not CNOOC will protect jobs and keep Nexen's head office in Canada. "It is also unclear how Canada's environmental standards will be enforced with regards to the sustainable development of its resources," it said.

"The Conservatives failed to act in good faith and inform the public of the consequences of this takeover. We're talking about a company that plays a key role in a critical sector of our economy," NDP natural resources critic Peter Julian said.

He said investment in Canada must not be at the cost of quality jobs and sustainable development of the country's resources.

The Conservative-dominated House of Commons rejected an NDP motion on Wednesday that demanded public consultations on the CNOOC deal. The vote was 145 against the motion to 125 for it.

(Reporting by David Ljunggren and Randall Palmer; Editing by Peter Galloway)

((david.ljunggren@thomsonreuters.com)(+1 613 235 6745)(fax +1 613 235 5890)(Reuters Messaging: david.ljunggren@thomsonreuters.com))