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July 15 (Reuters) - BlackRock BLK.N reported a 20% jump in second-quarter profit on Wednesday, as a stock market rally lifted the value of client assets.

The world's largest money manager's profit was $1.91 billion, or $12.19 per share, in the three months ended June 30, compared with $1.59 billion, or $10.19 per share, a year earlier.

Major U.S. equity indexes finished June with their biggest quarterly gains since 2020 as optimism grew over corporate earnings and investors looked beyond the volatility sparked by the conflict in the Middle East.

The benchmark S&P 500 index .SPX, a gauge of large-cap U.S. equities, gained 15% in the second quarter.

Assets managed by the New York-based firm rose to $15.34 trillion in the quarter, up from $12.53 trillion a year earlier and $13.89 trillion in the first quarter.

Assets under management mainly depend on two factors - the performance of investments and money flowing in and out of the funds.

Shares of the New York-based firm rose 1.6% in premarket trading. The stock has slipped 4% through last close, underperforming broader markets.