Aug 29 (Reuters) - Canada's merger court asked the competition bureau to pay about C$13 million ($9.58 million) to Rogers Communications and Shaw Communications for the lengthy court battle after its failed attempt to block the telecom firms' C$20-billion merger.

The Competition Tribunal, Canada's merger court, in a ruling dated Aug. 28 said the Commissioner of Competition Matthew Boswell's approach to block the deal was "unreasonable".

The companies maintained that Boswell "adopted an unnecessarily contentious approach throughout the litigation, which significantly increased the costs that they were required to incur," the tribunal said.

The Rogers-Shaw merger had faced intense opposition from Canada's antitrust regulator whose efforts to block it were rejected by the Competition Tribunal and a Canadian court.

The bureau's biggest concern was the deal would lessen competition in a country where wireless bills are already among the highest in the world.

In March, Canada approved Rogers' buyout of Shaw Communications after securing binding commitments to pay financial penalties if it failed to create new jobs and invest to expand its network.

($1 = 1.3571 Canadian dollars) (Reporting by Nilutpal Timsina and Shivani Tanna in Bengaluru; Editing by Sherry Jacob-Phillips)