JOHANNESBURG/LONDON (Reuters) - South Africa's competition watchdog wants to extend the deadline again for its investigation of Anheuser-Busch InBev's (>> Anheuser-Busch Interbrew) planned $106 billion takeover of SABMiller (>> SABMiller plc), raising the possibility of a delay for the beer industry's biggest-ever deal.

"This transaction raises certain concerns which should be considered and addressed," Competition Commission spokesman Itumeleng Lesofe told Reuters on Monday. "It is for this reason that we need more time to evaluate the transaction."

The watchdog had been due to finish its investigation on Tuesday but Lesofe said it can secure an extension of up to 15 days. It has already extended the deadline three times.

Drawn-out scrutiny by the South African regulator could frustrate the Budweiser brewer's goal of completing the acquisition in the second half of 2016 and delay reaping the financial benefits of combining the world's No.1 and 2 brewers.

Lesofe did not give any details on specific concerns.

A spokeswoman for AB InBev, maker of Budweiser and Stella Artois, had no immediate comment.

South Africa has a history of delaying takeovers or foisting onerous conditions, because competition authorities have a public interest mandate to safeguard jobs, in addition to an anti-trust mandate to protect competition.

In 2011, the regulator told U.S. retailer Wal-Mart Stores (>> Wal-Mart Stores, Inc.) not to cut jobs for two years following its acquisition of South African retailer Massmart (>> Massmart Holdings Limited), delaying implementation of the $2.4 billion deal by at least two months.

Analysts believe AB InBev wants to close the deal as soon as possible.

"The financial benefits of closing early are primarily earlier access to synergies, the absence of the pre-funding charge in 2016 and the possibility of not paying SAB's final dividend," Nomura analysts said in a research note. From an operational perspective, an earlier closing would reduce the risk of "business drift" in SAB's operations, they said.

A 15-day extension is not significant, said Bernstein Research analyst Trevor Stirling, but he said a close eye was needed on events moving forward.

"Does the Commission need more extensions? Does the Tribunal end up holding public hearings? Is there an appeal to the Competition Appeal Court? Those are all the things that would be significant," he said.

The Commission investigates deals for any antitrust issues and submits its views to the Competition Tribunal, which makes a final ruling on whether a deal should go ahead.

Since the deal was announced in November, AB InBev has completed a secondary listing on the Johannesburg Stock Exchange, lined up debt financing and addressed anti-trust concerns in the United States, Europe and China with proposed asset sales.

Formal regulatory approval in those markets is still required.

(Editing by Tiisetso Motsoeneng and Susan Fenton)

By Nqobile Dludla and Martinne Geller