Average U.S. long-term mortgage rates continued to tick down this week, remaining close to yearlong lows.

Mortgage company Freddie Mac says the nationwide average for a 30-year mortgage slipped to 3.99 percent from 4.01 percent last week. Rates have stayed around 4 percent for roughly the past month, after having opened the year at 4.53 percent.

Long-term mortgage rates fell as low as 3.31 percent toward the end 2012, as the Federal Reserve rolled out a since-ended program to purchase bonds in order to lower rates. They plunged in recent weeks amid economic slowdowns in Europe and China and the start of a recession in Japan.

The average for a 15-year mortgage, a popular choice for people who are refinancing, fell to 3.17 percent from 3.20 percent.