Senate blocks measure to forbid buys of Iran 'heavy water'

WASHINGTON (AP) - The Senate has blocked a Republican measure aimed at undercutting President Barack Obama's landmark nuclear deal with Iran.

Senators on Wednesday stopped an amendment that would have prevented the United States from buying any more Iranian "heavy water." The 57-42 vote fell three short of the 60-vote threshold needed to advance the legislation.

Heavy water is not radioactive but has research and medical applications and can also be used to produce weapons-grade plutonium. The Obama administration bought 32 metric tons of heavy water from Tehran last month. The $8.6 million deal helps Iran meet the terms of the nuclear agreement.

The amendment's author, Senator Tom Cotton of Arkansas, opposed the nuclear deal and wants to ensure there are no additional heavy water purchases.