Constrained shopping ahead of a later Easter holiday this year led to flat to lower sales at U.S. chain stores in the last week of March, reports said on Tuesday.

Sales were unchanged in the week ended April 1 after dipping by 1.6 percent in the prior week, according to a report by the International Council of Shopping Centers and UBS Securities LLC.

According to a separate report, sales fell by 1.1 percent on a year-over-year basis for the week ended April 1, following a 2.2 percent rise in the prior week. The report was produced by Redbook Research, an independent company.

Last year the Easter holiday was three weeks earlier than in 2006, boosting sales in March. This year the holiday falls on April 16 and sales could pick up during the month.

This past week, sales once again reflected the Easter shift and the shifting weather patterns across the country, said Michael Niemira, ICSC's chief economist and director of research.

The week's soft performance reflected difficult comparisons with Easter last year, Redbook said. But the research company said retailers prefer a later Easter holiday when the weather is more likely to be warmer and while consumers are looking for seasonal merchandise and apparel.

Sales at U.S. retailers through March were down 3.2 percent when compared with the same period in February, Redbook said.

Wal-Mart Stores Inc. recently estimated its sales in March rose 1.3 percent. The estimate was at the lower end of its forecast of 1 percent to 3 percent growth, the company said on Saturday.

Wal-Mart, the world's largest retailer, also said it had expected the later Easter to dampen its March sales, but boost April's numbers.

(Additional Reporting by Chris Reese and Mark Weinraub)