"Detailed discussions with relevant agencies in Australia and the United States continue.
"We are committed to resolving issues raised during the approval process and we're confident that the outstanding issues will be resolved," said SingTel president and CEO Lee Hsien Yang.
"SingTel continues to be dedicated to acquiring Optus. The extension of the offer period process does not interfere with our commitment to providing current and future SingTel shareholders with a compelling investment opportunity," he added.
In a statement, SingTel said that, pending approval from the Foreign Investment Review Board, it is necessary to extend the offer period for one month. However, this extension should not be taken to imply that the conditions of the offer, including the Australian Treasurer's approval, will be satisfied by that time.
SingTel, which has offered to pay as much as AU$20 billion in cash, stock, bonds and assumed debt to buy Optus.
Optus currently operates defence satellites on behalf of the Australian government, raising concerns about national security information, should the carrier be sold to SingTel, which is majority owned by the Singapore government.
Canberra first voiced concern in April that SingTel's bid would give a foreign government access to information relating to national security.
