US regulators have secured a court order to freeze assets of traders accused of seeking more than $13 million through illegal trades ahead of China-based CNOOC's public bid for Canadian oil firm Nexen Inc.

A Manhattan federal court order issued Friday froze about $38 million in assets from Hong Kong-based Well Advantage Limited and other unknown traders after the US Securities and Exchange Commission accused them of stockpiling shares of Nexen stock "based on confidential information about the deal."

Well Advantage is controlled by businessman Zhang Zhi Rong, who the SEC said also controls another company that has a "strategic cooperation agreement" with CNOOC, a state-owned energy giant.

The proposed $15.1 billion takeover, which has yet to be approved by regulators, would be China's largest foreign investment and its largest energy deal, according to data firm Dealogic. Nexen shares jumped 52 percent on Monday, when the announcement was made.

Well Advantage made trading profits of $7 million, while the other unknown traders used accounts in Singapore to make profits of some $6 million by using non-public information about the impending purchase, according to the SEC.

The traders "engaged in an all-too-familiar pattern of misusing inside information to place extremely timely trades and profit handsomely from their illegal acts," said Sanjay Wadhwa, deputy chief of the SEC Enforcement Division's Market Abuse Unit.

"Despite the challenges of investigating misconduct in the US by trading accounts located overseas, we have moved swiftly to freeze the assets of these suspicious traders and will hold them accountable for their actions," he added in a statement.

While Nexen currently has debts of about $4.3 billion, the deal is likely to face scrutiny from regulators across a range of countries due to the Chinese government's involvement.

China is the biggest energy consumer in the world, the second-biggest consumer of oil and has been snapping up resource assets across the globe in order to fuel break-neck growth.