"The situation will change if Iran can't sell oil," said Larijani to reporters on Wednesday.
Larijani did not elaborate on what those changes would be.
In order for Europe to help Iran with its oil exports and international banking, Iran must be able to sell oil, Larijani added.
Recent estimates put Iran's oil exports below 400,000 barrels per day due to US sanctions imposed in November, less than half of April's level and down from at least 2.5 million bpd in April last year, according to Reuters.
A senior US official said in March that Tehran had lost $10 billion in revenue since sanctions were reimposed.
Iranian President Hassan Rouhani said that Japan intends to keep buying Iranian oil, after meeting with Japanese Prime Minister Shinzo Abe in Tehran on Wednesday, according to Reuters. Abe did not confirm this statement.
"Iran will remain committed to the deal, which is important for the security of the region and the world. Tehran and Tokyo both oppose nuclear weapons," said Rouhani. "Iran will never initiate a war but will give a crushing response to any aggression."
Abe's visit is the first by a Japanese leader to Iran since its 1979 Islamic Revolution.