The pace of Americans signing contracts to buy homes picked up last month, rebounding from a drop in January. But a shortage of homes on the market continues to weigh on the housing market.

The National Association of Realtors said Wednesday that its pending sales index rose 3.1 percent in February to 107.5 after tumbling 5 percent in January. Despite the uptick, the index is still down 4.1 percent from a year earlier.

Lawrence Yun, chief at economist at the association, blamed the uneven performance on a shortage of houses for sale. "The minuscule number of listings on the market and its adverse effect on affordability are squeezing buyers and suppressing overall activity," he says.

Pending sales surged 10.3 percent in the Northeast, rose 3 percent in the South but eked out gains of just 0.7 percent in the Midwest and 0.4 percent in the West.

A shortage of inventory and healthy demand is pushing up housing prices. On Tuesday, Standard & Poor's said that its S&P CoreLogic Case-Shiller national home price index climbed 6.2 percent in January from a year earlier on top of a 6.3 percent annual gain in December.

A strong job market has given American consumers, including young millennials, the confidence to shop for homes, but the scarcity of choices means they face fierce competition as the spring home-buying season begins.