The semiofficial Fars News Agency said it learned that a Greek tanker returned to port empty after Iran refrained from loading its cargo for the financially troubled country.
The report notes other oil-rich countries have refrained from dealing with Greece.
"Greece would be particularly affected by oil sanctions as other exporters have refused to deal with Greek traders," the FNA report stated.
Iran's decision last week to halt crude oil exports to the United Kingdom and France sent oil prices to nine-month highs. The European Union set a July 1 deadline for an Iranian crude oil embargo, though Iranian lawmakers voted to pre-empt the EU move.
Tehran summoned many of its European envoys to protest what it said was an unfair response to what it describes as a peaceful nuclear program. U.N. inspectors last week expressed frustration regarding cooperation following their most recent visit to Iran.