DUBAI, Feb 25 (Reuters) - Iran's rial currency sank to a record low against the U. Foreign exchange traders say the rial's depreciation stems partly from the unrest and Iran's increased isolation in the face of Western sanctions over its human rights record and Russia's use of Iranian-made drones in Ukraine. sanctions in 2018 by then President Donald Trump have harmed Iran's economy by limiting Tehran's oil exports and access to foreign currency