The Financial Services Agency (FSA) on Thursday asked an expert panel to review takeover regulations, following a sharp rise in unrestricted stake-building on the market which has led to unsolicited takeovers.

Currently, an acquirer is required to make a tender offer if it wants to buy more than a third of a company's shares off market.

However the rules do not apply to stake-building on the market, which experts say is a loophole that allows an effective takeover without other shareholders having a say on the acquisition.

The issue gained attention when Tokyo-listed Asia Development Capital (ADC) built up most of its 40% stake in printing press manufacturer Tokyo Kikai Seisakusho Ltd on market in a matter of weeks, enough to give it veto rights over important board decisions.

(Reporting by Makiko Yamazaki; Editing by Sonali Paul)