Dubai World spent $80 a share, more than $2 billion, to acquire its current stake of almost 25 million shares in MGM Mirage. On Tuesday, shares of the company closed at $57.80 on the New York Stock Exchange, down 8 cents or 0.14 percent.

Gaming law in Michigan, where MGM Mirage operates the MGM Grand Detroit, requires prior approval before an investor exceeds 10 percent ownership in a casino company.

"The board unanimously approved the application. This will allow Dubai World to increase its stake in MGM if it wishes," Eric Bush, administrative manager for the Michigan Gaming Control Board told Zawya Dow Jones Tuesday.

Nevada gaming regulators don't require prior approval, but an investor must file a licensing application with the state once the 10 percent threshold is crossed. Dubai World applied for a gaming license with Nevada last year because of the investment arm's 50 percent ownership of CityCenter. Gaming Control Board member Mark Clayton said Tuesday a licensing investigation is under way.

Dubai World bought its stake in casino operator MGM Mirage last year, initially taking a 4.9 percent ownership that increased to 9.4 percent in February.

"Our company is encouraged by the Dubai World investment, as it expresses further confidence in our company and our brands," MGM Mirage Chief Financial Officer Dan D'Arrigo said in an e-mailed statement. "We look forward to a successful, long-term relationship."

Contact reporter Howard Stutz at hstutz@reviewjournal.com or 702-477-3871.