France, Britain, Germany, the United States, Russia and China made the revised offer to Iran last month, and Iran sent a reply to EU foreign policy chief Javier Solana last week.
"There was no mention of a suspension of sensitive activities in this letter," French Foreign Ministry spokesman Eric Chevallier told a news conference, using an expression that refers to enrichment-related activities.
Iran says it only wants to master nuclear technology to generate electricity. The U.N. Security Council has, however, imposed three rounds of sanctions on Iran for ignoring its demands to suspend enrichment and other activities.
Iran's ambassador to France handed French Foreign Minister Bernard Kouchner a copy of Iran's letter on Monday, Chevallier said.
"We will examine it collectively among the six of us and then think about a common position," he said, referring to the group of six countries.
"The fact that there is no mention of the suspension of sensitive activities is an issue, clearly," Chevallier said, adding that France still hoped to continue dialogue with Iran.
(Reporting by Francois Murphy)
