Investors poured almost $1 billion into Fidelity Investments’ two zero-fee index funds in their first month of operation.

The Fidelity Zero Total Market Index Fund attracted $753.5 million through Aug. 31, while the Fidelity Zero International Index Fund gathered $234.2 million, according to Fidelity’s website.

Fidelity’s unveiling of the funds Aug. 1 is the latest chapter in an ongoing price war for assets that track indexes. Vanguard Group, BlackRock Inc. and Charles Schwab Corp. have all been slashing fees on passive products to as little as a few pennies per $100 invested.

Fidelity has been matching rivals step for step. Although the firm built its reputation on the strength of its stock pickers, the Boston-based company has been aggressively pursuing passive assets, which have doubled to about $400 billion over the past three years. Fidelity’s largest stock fund is now an index fund, the $165 billion Fidelity 500 Index Fund.

So far none of Fidelity’s rivals have chosen to match its zero fee offer.