Pending home sales in the US increased 6.7% in May, reaching a six year high, according to data just released by the National Association of Realtors (NAR).

The Pending Home Sales Index increased to 112.3 from the revised 105.2 in April and is 12.1 higher than May 2012. Reflecting only contracts and not closings, pending sales are at the strongest level since December 2006, NAR reported.

Pending sales have been above year-ago levels for the past 25 months. The latest jump in contracts could be an effect from increasing mortgage rates and pent-up demand.

NAR chief economist Lawrence Yun said in a statement: “Even with limited choices, it appears some of the rise in contract signings could be from buyers wanting to take advantage of current affordability conditions before mortgage interest rates move higher.”

Yun expects the national median existing-home price to increase by more than 10% to almost $195,000 this year, representing the strongest increase since 2005.