May 9 (Reuters) - Australian broadband services provider TPG Telecom Ltd said on Monday it will sell its mobile tower and rooftop infrastructure assets to Canada's OMERS Infrastructure Management Inc for A$950 million ($670 million).

The sale of the passive infrastructure assets, which include more than 1,200 sites and form nearly a fifth of TPG's mobile network footprint, will deliver net cash proceeds of A$890 million, which will be used to repay bank debt, it said.

Passive infrastructure includes sites, buildings, towers, masts and poles, and excludes digital capabilities in active telecoms networks.

"The transaction represents competitive long-term financing, which will reduce our total financial leverage and deliver lower borrowing costs," TPG Chief Executive Iñaki Berroeta said.

The sale is the latest in a flurry of telecom sector deals in Australia, where firms are increasingly reviewing options for their aging infrastructure to reduce debt and try to capitalise on growth in 5G.

The country's largest telecom firm Telstra last year agreed to sell a 49% stake in its mobile tower business for A$2.8 billion. Uniti Group last month also agreed to a A$3.6 billion takeover.

Toronto-based OMERS had C$32 billion ($24.8 billion) in assets under management and investments in 12 countries at the end of last year, according to its website.

The deal marks OMERS' first fully owned Australian investment and its first foray into digital infrastructure in the Asia-Pacific region. It has already invested in German wholesale fibre company Deutsche Glasfaser and France's XP Fibre.

"Australia and Asia-Pacific more broadly are priority markets for OMERS, where we continue to see significant investment opportunities," OMERS said in a statement.

TPG said it will book a gain of about A$350 million to A$400 million after tax from the deal.

The deal is subject to approval from Australia's Foreign Investment Review Board and is expected to close in the third quarter of fiscal 2022, TPG added.

Shares in TPG traded roughly flat at A$5.54 by 0021 GMT, while the broader market fell nearly 1%.

($1 = 1.4178 Australian dollars) ($1 = 1.2915 Canadian dollars) (Reporting by Himanshi Akhand in Bengaluru; Editing by Daniel Wallis, Kim Coghill and Kenneth Maxwell)