FRANKFURT (Reuters) - German liquid crystal maker Merck KGaA (>> Merck KGaA) has extended the offer period for its planned takeover of Britain's AZ Electronic Materials (>> AZ Electronic Materials Group) for a third time because Chinese antitrust regulators have yet to give their approval.

Shareholders now have until February 28 to tender their stock. The previous offer period would have expired on February 18.

Merck, the world's largest maker of liquid crystals used in TVs, tablet and smartphone screens, agreed in December to buy AZ for $2.6 billion to expand its range of specialist chemicals for hi-tech gadgets.

"The decision to extend the timetable has been made with a view to allowing (Chinese Ministry of Commerce) MOFCOM to complete its review period in the ordinary course," Merck said on Friday after the market close.

It said 53.37 percent of AZ shares had been tendered as of 1300 GMT on Friday, down from 56.48 percent announced on February 6, indicating that some investors had withdrawn. It has made its offer contingent on securing at least 95 percent of the share capital.

AZ's share price has so far suggested that investors are confidence the deal is on track. Before Friday's announcement, the stock closed at 394.5 pence, 2.2 percent below Merck's offer of 403.5 pence per share.

(Reporting by Ludwig Burger; editing by Tom Pfeiffer)

Stocks treated in this article : Merck KGaA, AZ Electronic Materials Group