Fewer people are buying resale properties in the U.S., mainly because there is a shortage of housing on the market, new figures show.

According to the National Association of Realtors (NAR), existing home sales decreased 2.8% to a seasonally adjusted annual rate of 5.49m units, owed largely to the fact that the supply of residential properties on the market is currently at its lowest level since 1999.

Despite the decline in sales, following three consecutive months of increases, the U.S. housing market remains strong, supported by falling unemployment levels and a strengthening economy.

“The dip in housing sales is more a sign of the lack of homes to be bought than the desire to buy homes,” Joel Naroff, chief economist at Naroff Economic Advisors in Pennsylvania, told the press.

Last month, the number of residential properties on the market dropped by 10.8% from November to 1.65m units, owed in part to a lack of housebuilding, which is currently running just above a 1.2m unit rate.

The NAR estimates housing starts and completions should be in a 1.5m to 1.6m range to alleviate the severe shortage, but builders continue to complain about a shortage of skilled workers and land.

The lack of homes on the market is placing upward pressure on property prices, with the average price of a home increasing by 4% to $232,200 (£185,440) in December compared with the same month a year earlier.