The Internal Revenue Service announced on Tuesday that it will delay the start of the 2014 tax filing season by as much as two weeks due to delays caused by the recent closure of the federal government.

Citing the need for “adequate time to program and test tax processing systems,” the service announced that it expected a one- to two-week delay in the start of tax season, and that it would start accepting and processing 2013 individual tax returns no earlier than Jan. 28, 2014, and no later than February 4. Tax season had been expected to start on January 21.

Acting Commissioner Danny Werfel said in the statement that the service was exploring options to shorten the expected delay, but also noted, “Readying our systems to handle the tax season is an intricate, detailed process, and we must take the time to get it right. The adjustment to the start of the filing season provides us the necessary time to program, test and validate our systems so that we can provide a smooth filing and refund process for the nation’s taxpayers.”

The 16-day government shutdown came during the peak period for preparing IRS systems for the upcoming tax season, which involves programming, testing and deployment of more than 50 systems.

About 90 percent of IRS operations were closed during the shutdown, with some major workstreams closed entirely, and the IRS noted that it is also facing extra demands due to the need for systems to prevent refund fraud and ID theft — and that it is still dealing with a backlog of over 1.4 million pieces of correspondence that piled up during the shutdown.

The official start date will be announced in December.