* Firms agree to extend exclusive talks till Aug 31
* Bharti, MTN say terms may be adjusted
* Combined firm would be world's third-biggest telecoms firm
* Bharti shares flat in steady market, off day's highs (Adds details, quote, shares)
NEW DELHI, Aug 3 (Reuters) - Bharti Airtel and MTN Group extended their exclusive talks by a month aimed at merging their operations to create the world's third-largest mobile operator.
In separate statements issued on Monday, Bharti and MTN said the structure and terms of the potential transaction may be adjusted to reflect further discussions between the parties.
"As discussions between the parties regarding the potential transaction are continuing, both parties have agreed to extend the exclusivity period," Bharti, India's top mobile operator, said in a statement.
Shares in Bharti ticked up 0.3 percent by 0510 GMT in a steady Mumbai market, but were below the day's highs.
"Maybe they need more time to agree on the deal structure, total payment," said R.K. Gupta, managing director at New Delhi-based Taurus Asset Management.
"At this stage, there is not much clarity. But a sweetened offer cannot be ruled out as some MTN shareholders want Bharti to pay more," he said.
Bharti and MTN revived merger talks in May, a year after previous talks broke down over who would control a merged entity. A merger would create an emerging markets giant with more than 200 million customers across India, Africa and the Middle East. A combined entity would be the third-biggest mobile operator based on subscribers, behind China Mobile and Vodafone, although its annual sales of $20 billion would be dwarfed by China Mobile's $60 billion and Vodafone's $65 billion.
The exclusive talks over the deal, which would see Bharti and MTN pay cash and stock for a stake in the other, were due to end on July 31. Earlier sources had told Reuters the talks were likely to be extended by at least two to three weeks.
Under the initial terms, MTN and its shareholders would take 36 percent economic interest in Bharti Airtel and the Indian firm would end up with 49 percent of MTN.
The deal would give both firms exposure to new markets ripe for growth, while a full merger, the eventual aim of the talks, would yield cost savings, allow for technology sharing, and provide the financial muscle for more expansion, analysts say.
Standard Chartered was advising Bharti Airtel, while Bank of America Merrill Lynch and Deutsche Bank were advising MTN. ($1=47.8 rupees) (Reporting by Devidutta Tripathy; Editing by Ranjit Gangadharan and Anshuman Daga)