UPDATE 1-Brookfield includes all-cash option in Inter Pipeline offer

(Adds details on revised offer, background)

June 18 (Reuters) - Brookfield Infrastructure Partners on Friday revised its buyout offer for Inter Pipeline Ltd to include an option for an all-cash consideration, instead of a mix of cash and stock.

Brookfield's revision comes as the investment firm tries to beat a rival bid from Pembina Pipeline Corp, which has been recommended by Inter's board.

Pembina has an all-stock bid of about C$8.3 billion ($6.71 billion), while Brookfield had offered C$8.48 billion with 74% cash.

On Friday, Brookfield said Inter shareholders may now elect to get C$19.50 in all cash per Inter share, or 0.225 of Brookfield's class A share, valued at C$19.99 per Inter share as of Thursday's close.

Brookfield also said it was prepared to raise its offer by up to C$0.901 per Inter share, to C$20.401 per Inter share, pending the outcome of its challenge before the Alberta securities regulator.

The company last week filed an application with the regulator to do away with Inter's C$350 million termination fee to Pembina, saying it would increase its takeover offer for Inter if the fee was reduced or eliminated. ($1 = 1.2363 Canadian dollars) (Reporting by Arathy S Nair in Bengaluru; Editing by Devika Syamnath)