WASHINGTON, July 16 (Reuters) - Contracts to purchase previously owned U.S. homes fell more than expected in June as higher mortgages and house prices pushed prospective buyers to the sidelines.

The pending home sales index tumbled 5.4% last month to 72.5, the National Association of Realtors said on Thursday. Economists polled by Reuters had forecast contracts, which become sales after a month or two, falling 0.5%. Contracts fell in all four regions. They slipped 0.3% year-on-year in June.

Mortgage rates are likely to remain elevated amid renewed hostilities between the United States and Iran following the collapse of a fragile ceasefire last week.

"The highest mortgage rates in nearly a year and the record-high national median home price together are contributing to a tepid housing market that is especially difficult for first-time homebuyers," said Lawrence Yun, the NAR's chief economist.