The Pimco Total Return Fund, the world's largest bond fund, had $7.7 billion in net cash outflows in August, marking the fourth straight month of withdrawals from the fund, estimated data from Morningstar showed Wednesday.

Outflows from the fund, which is run by Pimco founder and co-chief investment officer Bill Gross, lowered the fund's assets to $251 billion at the end of August, the investment research firm said.

The fund's assets have fallen by $41 billion from $292 billion since the end of April. The latest monthly withdrawals also marked an increase from outflows of $7.5 billion in July.

Investors withdrew cash from bond funds in August on expectations of a pullback in the Federal Reserve's $85 billion in monthly purchases of Treasuries and mortgage-backed securities.

Investors pulled $39.5 billion from bond mutual funds and exchange-traded funds in August through August 28, data from research provider TrimTabs showed.

Interest rates also rose on the worries surrounding the Fed. The yield on the benchmark 10-year U.S. Treasury note hit a two-year high of just over 2.93 percent on August 22. Treasury yields move inversely to prices.

The Pimco Total Return Fund had 39 percent of its holdings in U.S. government-related securities at the end of July, data from the firm's website has shown.

The Newport Beach, California-based Pacific Investment Management Co., a unit of European financial services company Allianz SE, had $1.97 trillion in assets as of June 30, according to the firm's website.

The DoubleLine Total Return Bond Fund, meanwhile, had $1.13 billion in estimated outflows in August, marking its third straight month of withdrawals from the fund.

The outflows from the fund, run by Jeffrey Gundlach, accelerated after withdrawals of $580 million in July. The latest outflows also lowered the fund's assets to roughly $36.8 billion, the Chicago-based Morningstar said.

The Los Angeles-based DoubleLine Capital, where Gundlach serves as chief executive and chief investment officer, oversees roughly $57 billion in assets.

(Editing by James Dalgleish, Jennifer Ablan and Chris Reese)