Economists say a combination of natural and man-made disasters led to unexpectedly weak U.S. retail sales in the crucial two months before Christmas.

MasterCard Advisors SpendingPulse, which tracks retail spending, reports that sales rose just 0.7 percent over the same October-to-December period last year.

MasterCard says October's Superstorm Sandy affected sales in the Northeast while the murders of 20 schoolchildren and six teachers in Connecticut earlier this month put many people out of the spending mood.

It also says the looming “fiscal cliff” on January 1, with its package of tax hikes, is making many people reluctant to spend.

Many U.S. retailers depend on strong holiday sales for a successful year.