U.S. mortgage application activity rose to its strongest level in six weeks even as 30-year home borrowing costs jumped to their highest levels since March, the Mortgage Bankers Association said on Wednesday.

The Washington-based group said its index on mortgage requests rose 4.1 percent to 406.3 in the week ended Jan. 12, which was the highest since 408.3 in the Dec. 1 week.

Average interest rates on 30-year conforming mortgages, or loans with loan balances of $453,100 or less, increased to 4.33 percent, up 10 basis points from the prior week. This was highest since 4.34 percent in week of March 31.