WASHINGTON (Reuters) -U.S. mortgage rates increased to a four-month high this week and could rise further amid fears that President-elect Donald Trump's proposed economic policies could stoke inflation.

The average rate on the popular 30-year fixed-rate mortgage climbed to 6.79%, the highest level since July, from 6.72% last week, mortgage finance agency Freddie Mac said on Thursday.

It has increased for six straight weeks and has risen by 71 basis points since late September.

As supply remains below pre-pandemic levels, rising mortgage rates and elevated house prices have combined to stifle sales of previously owned homes, which hit a 14-year low in September.

"Buyers who were waiting until after the election to get into the market may not see rates as low as they had hoped," said Lisa Sturtevant, chief economist at Bright MLS.

The 30-year fixed mortgage rate tracks the benchmark 10-year Treasury note, whose yield jumped to a four-month high in the aftermath of Republican Trump's victory in the U.S. presidential race. Trump campaigned on a platform of tax cuts, which economists say would juice the economy, widen budget deficits and increase government borrowing.

He also promised to impose a 60% tariff on Chinese goods and at least a 10% levy on all other imports, which economists expect to re-ignite inflation and reduce the Federal Reserve's scope to cut interest rates.

Most home owners have mortgage rates below 4% and the so-called "rate lock" is starving the market for previously owned homes of supply. Bright MLS estimated that the median monthly payment on a mortgage to buy a $400,000 home has increased by almost $200 in just six weeks.

(Reporting By Lucia Mutikani; Editing by Aurora Ellis)