May 21 (Reuters) - Wall Street's main indexes opened lower on Thursday, as oil prices rose after Reuters reported that Iran's Supreme Leader Mojtaba Khamenei had ordered that highly enriched uranium not be moved out of the country, dampening hopes for progress in talks between Washington and Tehran.

The Dow Jones Industrial Average fell 25.5 points, or 0.05 percent, to 49,983.8 at the open. The S&P 500 declined 22.2 points, or 0.30 percent, to 7,410.78, while the Nasdaq Composite lost 126.7 points, or 0.48 percent, to 26,143.616.