"Several of our systems are not currently operating, including our modernized e-file system and a number of other related systems," the IRS said in a statement.

"A number of taxpayer and tax practitioner tools are unavailable," it said. "IRS.gov remains available, although a number of the services on the site are not, including Where’s My Refund."

The agency said it is in the process of making repairs and anticipates some of the systems will remain unavailable until Thursday.

The IRS said it does not anticipate major refund disruptions. "We continue to expect that nine out of 10 taxpayers will receive their refunds within 21 days," the agency said.

(Reporting by Eric Beech; Editing by Eric Walsh)