The government may impose restrictions on off-hours stock trading in the wake of Livedoor Co.'s surprise acquisition of a large stake in a radio broadcaster last week, Financial Services Minister Tatsuya Ito said Tuesday.

"Depending on how you do it, off-hours trading on a stock exchange can take a form that looks similar to trading conducted outside a stock exchange," Ito said. "We need to study if off-hours trading should be covered by regulations concerning tender offers."

His comments indicate the government might revise the Securities and Exchange Law to regulate off-hours trading, which is now administered only by stock exchange rules.

On Feb. 8, Livedoor bought a 29.6 percent portion of Nippon Broadcasting System Inc. during premarket trading through the Tokyo Stock Exchange, bringing its stake in the radio broadcaster to 35 percent. The surprise move derailed a bid by Fuji Television Network Inc. to take over the firm and turn it into a subsidiary. Nippon Broadcasting is Fuji TV's top shareholder.

Ito said Livedoor violated no laws because off-hours trading is not regulated by the securities law.

Under the law, a company that intends to acquire more than a third of shares in a listed firm outside a bourse must do so by publicly launching a takeover bid, announcing beforehand the number of shares it plans to acquire and the purchasing price.

Ito said off-hours trading is designed to better serve investor needs and enhance the function of securities transactions, adding, "We need to closely observe whether the latest case poses any problems in light of reinforcing the securities market."

An official at the Financial Services Agency said he had never heard of a purchase as massive as Livedoor's being conducted in off-hours trading.