"We can't make it any more clear that we are committed to this campaign of maximum pressure and we are not looking to grant any exceptions or waivers," Brian Hook, the State Department coordinator on Iran, told reporters.

He added, however, that he has not yet seen a "concrete" French proposal and could therefore not comment on the idea.

French President Emmanuel Macron has been seeking to ease soaring tensions by bringing some economic relief to Iran and last month appeared to draw President Donald Trump's interest when Macron said he hoped to arrange a summit between the US leader and his counterpart Hassan Rouhani.

Iran has been threatening to take new actions to curb its compliance with a 2015 denuclearization deal, from which Trump withdrew last year as he reimposed punishing sanctions.

Iran is upset that it did not reap greater dividends from compliance but said it would be satisfied if it receives $15 billion in credit, which it would pay back through future oil sales.

Hook was speaking to discuss the latest volley of US sanctions on Iran, which target a shipping network that the Treasury Department said has sold millions of barrels of oil to Syria, benefiting President Bashar al-Assad and Lebanese militants Hezbollah.

Hook noted that the United States also imposed other sanctions on Iran on Friday and Tuesday and warned, "There will be more sanctions coming."