(Reuters) - The United States will likely suffer the loss of its triple-A credit rating from another major rating agency by the end of this year due to concerns over the deficit, Bank of America Merrill Lynch forecasts.

The trigger would be a likely failure by Congress to agree on a credible long-term plan to cut the U.S. deficit, the bank said in a research note published on Friday.

A second downgrade -- either from Moody's or Fitch -- would follow Standard & Poor's downgrade in August on concerns about the government's budget deficit and rising debt burden. A second loss of the country's top credit rating would be an additional blow to the sluggish U.S. economy, Merrill said.