Oil prices fell about 2% on Thursday as talks to resurrect a nuclear deal with Iran entered their final stages and could unlock more crude supplies, but losses were limited by tension between top energy exporter Russia and the West over Ukraine. "(The) oil market is locked in a tug of war between Iranian sanctions relief and Russian-Ukraine tensions," said Stephen Brennock at brokerage PVM Oil. However, tension over a possible Russian invasion of Ukraine continued to support oil markets because of the potential disruption to energy supplies.