Pending home sales continued to make gains last month, rising to the highest level since April 2006, according to the National Association of REALTORS®' Pending Home Sales Index, a forward-looking indicator based on contract signings. 

Read more: New-Home Sales Climb to 7-Year High

Large gains in pending home sales in the Northeast and West helped to offset small decreases in the Midwest and South. 

NAR's Pending Home Sales Index rose 0.9 percent in May to 112.6 in May. The index is at its highest level since April 2006 when it was 113.7.

"The steady pace of solid job creation seen now for over a year has given the housing market a boost this spring," says Lawrence Yun, NAR's chief economist. "It's very encouraging to now see a broad based recovery with all four major regions showing solid gains from a year ago and new home sales also coming alive."

Yun says this year's strong sales are causing home prices to rise to an "unhealthy and unsustainable pace."

"Housing affordability remains a pressing issue with home-price growth increasing around four times the pace of wages," says Yun. "Without meaningful gains in new and existing supply, there's no question the goalpost will move further away for many renters wanting to become home owners."

Here's a closer look at how the Pending Home Sales Index performed regionally in May:

• Northeast: rose 6.3 percent to 93.9 last month and is 10.6 percent above a year ago.
• Midwest: fell 0.6 percent to 111.4 but remains 7.8 percent above year ago levels. 
• South: dropped 0.8 percent to 127.8 but are still 10.6 percent above last May.
• West: rose 2.2 percent to 104.5 in May and are 13 percent above a year ago. 

Source: National Association of Realtors