NEW YORK (Reuters) - U.S. loan application activity for home purchases rose last week to its highest since early June even as borrowing costs increased for the first time in four weeks, according to Mortgage Bankers Association data released on Wednesday.

The Washington-based industry group said its seasonally adjusted measure of home mortgage applications rose to 243.2 in the week ended on Jan. 20, up 6.0 percent from the previous week.

Interest rates on 30-year, fixed-rate conforming mortgages, the most widely held type of U.S. home loan, averaged 4.35 percent, up from 4.27 percent in the prior week.

Conforming loans are those with balances of $424,000 or less and qualify for guarantees from federal mortgage agencies Fannie Mae <FNMA.PK> and Freddie Mac <FMCC.PK>.

Four weeks ago, 30-year conforming mortgage rates averaged 4.45 percent, their highest since April 2014.

U.S. home borrowing costs rose in step with bond yields <US10YT=RR> in a renewed selloff in the U.S. Treasuries market as investors assessed whether early actions from U.S. President Donald Trump would push up domestic growth and inflation.

The MBA's seasonally adjusted index on application activity to refinance an existing mortgage edged up 0.2 percent to 1,265.6.

The refinance share of overall mortgage application activity fell to 50.0 percent, its smallest since July 2015, from 53.0 percent in the prior week, the MBA said.

The group's seasonally adjusted of total mortgage applications increased 4 percent to 397.4, its highest in five weeks.

The latest week's data factored in an adjustment for the Martin Luther King Jr. holiday on Jan. 16.

(Reporting by Richard Leong; Editing by Chizu Nomiyama and Lisa Von Ahn)