NEW YORK (Reuters) - A measure of U.S. mortgage application activity fell last week to its lowest level since early January as 30-year mortgage rates rose to their highest since July 2015, data from the Mortgage Bankers Association showed on Wednesday.


The Washington-based industry group's seasonally adjusted mortgage market index fell 9.4 percent in the week ended Nov. 25 to 417.2, the lowest since 398.5 in the week of Jan. 8.


Excluding seasonal factors including the U.S. Thanksgiving holiday, weekly mortgage activity dropped 38 percent from the previous week, MBA said.


The interest rates on 30-year fixed-rate conforming mortgages averaged 4.23 percent, which was the highest since July 2015 and up from previous week's 4.16 percent.


Conforming loans are those with balances of $417,000 or less, which mortgage agencies Fannie Mae and Freddie Mac guarantee. <FNMA.PK> <FMCC.PK>


The average interest rate on 30-year fixed-rate jumbo mortgages with balances of more than $417,000 rose to 4.18 percent, up from 4.04 percent in the prior week and the highest since July 2015.

Mortgage rates have jumped in step with a surge in U.S. 10-year Treasury bond yields, which hovered at their highest levels since July 2015, following Donald Trump's surprise U.S. presidential election win.

Traders have bet on faster economic growth and inflation if Trump and the Republican-controlled Congress enact big tax cuts and federal spending.

The surge in mortgage rates, which have risen more than 0.40 percentage point since the Nov. 8 election, has slashed refinancing activity.

MBA's seasonally adjusted refinancing index fell 16 percent to 1,469.9 last week, its lowest level since early January.

The group's seasonal gauge on applications to buy a home, which is seen as a proxy on future home sales, dipped 0.2 percent to 233.60.

The average loan size for purchase applications reached $312,400, the highest since the MBA began its weekly survey in 1990.

(Reporting by Richard Leong; Editing by Chizu Nomiyama and Meredith Mazzilli)