WASHINGTON, March 26 (Reuters) - The average rate on the popular U.S. 30-year fixed-rate mortgage has jumped to a six-month high as rising oil prices from the dragging Middle East war fanned inflation worries, which could weigh on home sales during the typically busy spring season.

The 30-year fixed mortgage rate averaged 6.38%, its highest since early September and up from 6.22% last week, mortgage finance agency Freddie Mac said on Thursday. The rate has now increased for four straight weeks, undercutting efforts by the Trump administration to make housing more affordable.

It dropped to 5.98% on the eve of the Iran war after U.S. President Donald Trump ordered Freddie Mac and Fannie Mae to expand purchases of mortgage-backed securities. Oil prices have increased more than 30% since the conflict started at the end of February, boosting U.S. Treasury yields. 

Mortgage rates track the benchmark 10-year Treasury yield. Housing affordability has become ⁠an increasingly potent political issue ahead of the November midterm elections.