Iran's rial currency fell to near-record lows Thursday as concerns grew in Tehran that European nations will start a process to reimpose United Nations sanctions on the Islamic Republic over its nuclear program, further squeezing the country's ailing economy.

The move, termed the "snapback" mechanism by the diplomats who negotiated it into Iran's 2015 nuclear deal with world powers, was designed to be veto-proof before the world body and would be likely to go into effect after a 30-day window.