NEW YORK (CNNMoney.com) - Mortgage rates rose for the fourth consecutive week, to the highest level in nearly four years, Freddie Mac said Thursday.

The average rate on 30-year fixed-rate mortgages rose to 6.53 percent for the week ending April 20, up from the prior week's 6.49 percent, a Freddie Mac survey said. In the year-ago period, the 30-year mortgage averaged 5.80 percent.

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The level was the highest since the week of July 12, 2002.

"Mortgage rates drifted upward this week following the release of the Consumer and Producer Price Indexes for March, which came in at the upper end of market expectations for inflation," said Frank Nothaft, Freddie Mac vice president and chief economist, in a statement.

"As a result of higher mortgage rates, housing market activity is beginning to slow, as evidenced in the lower housing starts statistics for March."

The average rate on 15-year fixed-rate mortgages rose to 6.17 percent from 6.14 percent last week. A year ago, that loan averaged 5.36 percent.

Five-year adjustable-rate mortgages averaged 6.16 percent, up from 6.13 percent the prior week. The five-year ARM averaged 5.22 percent last year.

One-year adjustable-rate mortgages averaged 5.63 percent, up from 5.61 percent from the week before. At this time last year, the one-year loan averaged 4.26 percent.

"Even though lenders are offering greater interest rate discounts on ARMs, the interest rate savings has declined relative to fixed-rate mortgages," said Nothaft.

"The ARM share of applications dipped to 32 percent in March from 35 percent in November 2005, according to our survey. If the Fed continues to raise short-term rates, the ARM share will likely decline further."

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