WASHINGTON, June 23 (Reuters) - The Republican-majority U.S. Senate backed legislation on Tuesday to halt U.S. military action against Iran, but it was not immediately clear how it would affect the conflict as President Donald Trump's administration negotiates a peace agreement with the Islamic republic.

The Senate voted 50-48 in favor of the concurrent resolution, which passed the House of Representatives early this month, reflecting growing concern even among some of Trump's Republicans about the unpopular conflict that began on February 28.

(Reporting by Patricia Zengerle; additional reporting by Richard Cowan;)