Tehran's oil exports have risen since late 2020, despite US sanctions toughened under US President Donald Trump. Joe Biden's administration took office in January pledging to rejoin Iran's nuclear deal with world powers, which Trump had quit.
"China and Iran are carrying out normal economic and trade cooperation, including energy, within the framework of international law, and the relevant cooperation is reasonable and legitimate," the spokesperson said.
The move would be the first under the management of General Joaquim Silva e Luna, who replaced Roberto Castello Branco as the company's top executive after the government apparently disagreed with the state-run company's fuel pricing policy.
In a note on Friday, brokerage Ativa Investimentos said its model indicated a potential 13% rise in gasoline prices, driven by the increasing international oil prices.