LONDON, Jan 16 (Reuters) - U.S. private equity firm General Atlantic said on Tuesday it has agreed a deal to buy UK-based infrastructure investor Actis, in the latest sign of investors betting on growth in alternative assets.

The deal will grow General Atlantic's assets under management to around $96 billion, according to a joint statement by the two companies which did not disclose the financial terms of the deal.

The agreement comes days after BlackRock agreed a deal to buy Global Infrastructure Partners for $12.5 billion, putting the asset management giant at the heart of investing in ports, power and digital infrastructure projects globally.

Under General Atlantic's deal, Actis will become the firm's sustainable infrastructure arm, adding around $12.5 billion in assets specialising in energy transition, digital transition, and supply chain transformation, the companies said.

"Addressing the global paradigm shift toward sustainability requires an economic transformation and a capital investment on a massive scale. With the addition of Actis, we are taking a significant step forward," said Bill Ford, chairman and CEO of General Atlantic.

Actis will continue to be led by its chairman and senior partner Torbjorn Caeser and its funds will operate under the existing Actis brand, the statement said.

General Atlantic, founded in 1980, currently holds a portfolio of 225 companies, including fast-fashion retailer Shein, India's digital payments startup PhonePe and self-driving technology firm Mobileye, its website showed. (Reporting by Gokul Pisharody in Bengaluru and Iain Withers in London; Editing by Savio D'Souza and Susan Fenton)