Shares of the Australian energy infrastructure firm jumped as much as 5.7% to a record high of A$2.61, with Brookfield's latest cash offer valuing AusNet at A$2.65 a share, topping a more complex A$2.60-per-share bid by APA in late September.

With the binding agreement, AusNet said it ended APA's due diligence access, but added the gas pipeline operator was looking at whether it could increase the cash component of its bid after it was told Brookfield may revise its own.

"APA did not indicate that it would be able to offer a full cash alternative or the value level at which any improvement to its indicative proposal could be made," AusNet said in a statement.

In response, APA said in a statement it still considered AusNet "highly attractive" but did not confirm if a new offer was forthcoming.

While the agreement includes a provision to terminate their deal if a better offer emerges, AusNet said it also included an A$101.7 million break fee.

Brookfield's offer also has the backing of Singapore Power Group and its 32.74% AusNet stake, the company said.

AusNet opened its books to APA after a government panel in October ordered an amendment to an exclusive agreement between it and Brookfield.

($1 = 1.3308 Australian dollars)

(Reporting by Harish Sridharan in Bengaluru; Additional reporting by Nikhil Kurian Nainan; Editing by Diane Craft, Peter Cooney and Ramakrishnan M.)