BOSTON – Fidelity Investments said Thursday it will cut nearly 1,300 jobs this month, with more layoffs to come early next year, in response to declining markets that have eroded mutual fund assets along with the fees Fidelity earns from its core business.

Layoff notices will go out to about 2.9 percent of Fidelity’s overall work force of 44,400. The cuts will be spread across the company’s far-flung U.S. operations, affecting management positions as well as lower-level jobs, said Anne Crowley, a spokeswoman for Boston-based, privately held Fidelity. No fund managers or analysts are being laid off, she said.

A second round of layoffs is planned in the first three months of next year, with the number of those cuts and other details to be released in coming weeks.

Crowley declined to offer specifics but said both rounds of cuts will cumulatively affect fewer than 4,000 jobs – a figure that had circulated recently in media accounts.

In a letter distributed to employees Thursday, Fidelity President Rodger Lawson said recent market volatility has hurt company revenue and “has led me to conclude that many of the cost improvement plans which would have been phased in by our business units over the next three years need to be accelerated.”

Crowley said the cuts are being made “based on decisions by individual business leaders on what their needs are. Most of them are doing some layoffs in their divisions.”

In addition to its 11,000-employee Massachusetts operations in Boston and Marlborough, Fidelity has sizable offices in Florida, Kentucky, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Rhode Island, Texas and Utah.

The first round of cuts will be roughly proportionate at those locations, or around 2.9 percent, Crowley said.

The cuts are in addition to reductions totaling about 800 jobs in two rounds earlier this year after Fidelity reorganized some business units. Those reductions came largely in Fidelity’s personal and workplace-investing operations that oversee other companies’ pensions and 401(k) plans.

Reeling markets made staff at Fidelity’s more than 400 mutual funds targets for job cuts as well. According to Financial Research Corp., assets at Fidelity’s funds had lost nearly 23 percent of their value through October of this year, to nearly $717 billion. The total excludes money-market funds, an area in which Fidelity is the industry leader based on more than $400 billion in assets. Overall, Fidelity managed $1.4 trillion as of Sept. 30.

“All of our mutual fund competitors are experiencing the same type of declines,” Crowley said. “We have a strength many of our competitors don’t have. We have a huge money-market operation, and those funds have been attracting new customers and new assets over the last several months.”