Marking another milestone in a year of brisk growth, assets of money market mutual funds broke past $700 billion last week.

The Investment Company Institute said these funds grew 0.9% in the week ending July 5, to $705.52 billion.

Money market assets have been climbing all year, as investors have fled the bond market. Because money market funds strive to maintain a stable net asset value of $1 per share, they are generally considered a safe haven during periods of market turbulence.

Right now, it appears that money funds "are being used as a holding bin" by investors who are shifting money from bonds to equities, said a spokeswoman for the institute, a Washington-based trade group for mutual fund companies.

Assets of retail money market funds totaled $494.97 billion in the week through July 5, up $5.54 billion. Funds for institutional investors held $210.55 billion, up $773 million.

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