NEW YORK — Moody’s Investors Service lowered the credit ratings of 15 of the world’s largest banks late Thursday, including Bank of America, JPMorgan Chase and Goldman Sachs, saying their long-term prospects for profitability and growth are shrinking.

The ratings agency said it was
especially concerned about banks
with significant financial markets businesses because those markets have become so volatile. Some of the largest European banks were also downgraded, including Barclays, Deutsche Bank and HSBC.

The downgrades mean Moody’s is more concerned about the ability of
the banks to repay their debts. Moody’s had said in February that it was considering downgrading the credit ratings
of major banks in the U.S. and in Europe.

A downgrade usually means that it becomes more costly for banks to raise money by selling debt. Investors demand higher interest for riskier debt, which is what the downgrades represent. However, with interest rates already at rock-bottom levels, the downgrades may not affect the cost of funding for the banks that much.

The stock market has also priced
in any negative impact from the
ratings downgrades, according to Bert Ely, a banking consultant in the Washington, D.C. area. “They’ve been telegraphing this thing for months,”
Ely said.

In a sign that investors were taking the news in stride, stocks of major U.S. banks rose in after-hours electronic trading. Moody’s made its announcement after regular stock trading
had closed. Morgan Stanley rose the most,
3.3 percent, gaining
45 cents to $14.41. JPMorgan Chase rose
41 cents to $35.92 and Bank of America rose
12 cents to $7.94.

The downgrades come at a time of great uncertainty in the global economy. Europe’s currency union is under threat from bad bank loans. The U.S. economy is slowing and the fast-growing emerging economies of India, Brazil and China are also cooling. Financial markets have also been volatile.

On Thursday the Dow Jones industrial average plunged 251 points, its second-worst loss of the year, as new reports indicating slower manufacturing in the U.S. and China made investors fearful that the global economy could be heading for another slump.

Moody’s has been on a downgrading spree lately. In June Moody’s downgraded Spain by three notches, after downgrading 16 Spanish lenders in May. It also cut the ratings on seven German and three Austrian lenders in June.

Among the banks that were downgraded Thursday:

• Bank of America’s debt was downgraded to Baa2 from Baa1. That’s just a couple of notches above junk status.

• JPMorgan Chase’s debt was downgraded to A2 from Aa3

• Citigroup’s to Baa2 from A3

• Morgan Stanley’s to Baa1 from A2

• Goldman Sachs’s to A3 from A1

• HSBC’s to Aa3 from Aa2

• Barclay’s to A3 from A1