WASHINGTON, Jan 24 (Reuters) - Internal Revenue Service officials on Monday said some letters indicating how much U.S. taxpayers can expect to still claim for the 2021 child tax credit showed incorrect amounts, but added that they do not believe the problem is widespread.

The disclosure came as the IRS launched its annual individual tax return filing season, with an April 18 deadline.

Many Americans received the first half of an expanded 2021 child tax credit in monthly installments between July and December, with the remainder claimed when they file tax returns.

Earlier in January, the IRS sent out the "6419 letter" https://www.irs.gov/individuals/understanding-your-letter-6419 to taxpayers showing aggregate amounts of payments already received https://www.irs.gov/pub/irs-utl/ltr6419-sample.pdf through December.

But for some parents who moved or changed bank accounts in December, the letters may not show accurate amounts, affecting what they can still claim when they file tax returns, said Kenneth Corbin, chief taxpayer experience officer. He added that taxpayer login accounts on the IRS.gov website show accurate information, and taxpayers should claim the credit based on this or their own payment records.

The child tax credit for 2021 was $3,600 for each child under six years of age and $3,000 for each child aged 6 to 17, with July-December monthly payments of $300 and $250, respectively.

The increased amounts, part of COVID-19 rescue legislation, expired on Dec. 31 and revert to $2,000 per child under the age of 17 for 2022, claimable on tax returns filed in 2023. The Biden administration has proposed extending the expansion and monthly payments, but Democratic Senator Joe Manchin has opposed this provision.

IRS Commissioner Charles Rettig said he is "highly confident it is nowhere near millions or hundreds of thousands" of taxpayers affected by the glitch and cautioned the media not to create "unnecessary anxiety" among the public.

Rettig reiterated that to avoid delays, taxpayers should file electronically with direct deposit for their refunds. (Reporting by David Lawder Editing by Paul Simao)