(Read More: Pimco US mutual funds suffer record $14.5 billion outflows in June)
"So the #Fed #tapers with 1% or less #inflation & GNP growth? Policy rate still the key to value however. On hold 'til 2016," Gross wrote. Fifteen of the Fed's 19 policymakers in June had not expected to start raising rates until 2015 or later.
The Pimco fund also increased its holdings of mortgage securities to 36 percent in June, the most since last February, from 34 percent the prior month.
The fund was down 2.64 percent in June, marking its weakest monthly performance since September 2008, according to Morningstar. Investors pulled a record $9.6 billion from the fund last month, reducing its assets to roughly $268 billion, the Chicago-based Morningstar said.
The fund also showed a decrease in its holdings of non-U.S. developed market securities to 5 percent in June from 7 percent the prior month. Holdings of investment-grade and high-yield corporate bonds, as well as emerging market securities, were unchanged in June at 6 percent, 3 percent and 7 percent, respectively.
(Read More: Pimco's Gross: Don't jump ship on treasurys now)
The Barclays U.S. Corporate High Yield Index fell 2.62 percent in June, notching its weakest performance since September 2011.
The fund's exposure to "other" securities, which may include municipal and convertible bonds, preferreds, and Yankee bonds, was at 5 percent in June.
Pimco said on its website that its U.S. Treasurys and government-related holdings may include nominal and inflation-protected Treasurys, Treasury futures and options, agencies, FDIC-guaranteed and government-guaranteed corporate securities, and interest rate swaps.
Pimco has been in the spotlight because of its large exposure in Treasurys and Treasury-related securities, which have been under severe selling pressure this year. Gross has even sought to reassure his investors, touting Pimco's 40-year performance history.
The fund is down 3.11 percent so far this year, ahead of only 24 percent of peers, according to Morningstar. Since its inception in May 1987 through last Friday, the fund has earned an annualized return of 8.04 percent, above the 6.94 percent annualized return of the Barclays U.S. Aggregate Bond Index over that period.
(Read More: Pimco flagship fund loses big on bond stock)
Fed Chairman Ben Bernanke triggered the credit market selloff when he told Congress on May 22 that the central bank could reduce its bond-buying later this year if the U.S. economy looked strong enough. The yield on the 10-year U.S. Treasury has risen 92 basis points since its close of 1.62 percent on May 2. As yields rise, prices fall.
The Fed is buying $85 billion in Treasurys and agency mortgage securities monthly in an effort to spur hiring and lower long-term borrowing costs. The Fed's stimulus has been a major source of support for both the bond and equity markets.
The Pimco Total Return Exchange-Traded Fund, meanwhile, is down 2.26 percent for the year, ahead of 54 percent of peers, according to Morningstar. The ETF was down 2.21 percent in June, marking its weakest monthly performance since its launch in February 2012. The actively-managed ETF is designed to mimic the strategy of the flagship fund.
Investors pulled $511.5 million from the ETF in June, its biggest monthly outflow since inception. In the most recent week in July, investors pulled $52.4 million, Morningstar said. The ETF is still the largest actively-managed U.S. ETF with roughly $4.3 billion in assets, the investment research firm said.
On July 7, Gross tweeted: "1 to 2 month performance numbers are a blip on a 40-year performance history. PIMCO marches on a long-term path."
(Read More: Pimco Gross skewers Bernanke: You're part of the problem)
In his July letter to investors, Gross said that the bond market selloff was "overdone" and that the yield on the benchmark 10-year Treasury belonged at 2.2 percent. The yield on the safe-haven bond closed at 2.54 percent on Monday.
"Don't jump ship now. We may have reached an inflection point of low Treasury, mortgage and corporate yields in late April, but this is overdone," Gross wrote.
Pacific Investment Management Co., a unit of European financial services company Allianz SE, had $2.04 trillion in assets as of the end of March, according to the firm's website.
The Newport Beach, California-based firm is run by Gross and chief executive and co-chief investment officer Mohamed El-Erian.