Iran has cut oil exports to six European countries in retaliation against sanctions imposed by the EU and the US.
According to Iranian state TV, Tehran will scrap crude sales to France, Greece, Italy, Netherlands, Portugal and Spain.
"They are playing hard ball," Olivier Jakob, managing director of Swiss consultancy Petromatrix, told the Wall Street Journal. "Especially they cut exports to Greece, and Greece is importing about 50% of its crude from Iran."
The move comes days after Iran's oil minister, Rostam Qassemi, said Tehran could cut off oil exports to "hostile" European nations as tensions rise over the Islamic Republic's nuclear programme.
State TV also reported that Iran had launched a new generation of domestically made centrifuges at its Natanz uranium site. Western experts have expressed doubts, saying that the Iranians have been struggling to reach even second-generation centrifuges. The Islamic Republic has often overestimated its nuclear capabilities.