Germany and France on Monday reinforced a call for Iran to respond to concerns about its nuclear program in September or face tougher sanctions, and said they wanted wide international agreement on those measures. German Chancellor Angela Merkel pointed to a Group of Eight leaders' agreement in July to reevaluate their position on Iran at a G-20 summit in late September. President Barack Obama has set a Sept. 15 deadline for Iran to respond to US overtures about negotiating over its nuclear program. "Initiatives must be taken during the month of September which take account of Iran's will or otherwise to cooperate," French President Nicolas Sarkozy said after meeting Merkel. If it does not, he said, "Germany and France will be united in calling for a strengthening of sanctions." "Iran should know that we mean this very seriously," Merkel said. Teheran "must not again let the deadline elapse at will," she added. Merkel last week urged Iran to stop its nuclear program and return to negotiations in September, or risk facing stiffer sanctions "in the energy, financial and other important sectors." She declined to elaborate Monday on what form those sanctions might take or what they might target, other than to reiterate that the energy sector is a possibility. "I don't want to say anything about details now because that makes no sense - we must try to set these sanctions on the widest possible basis," she said. Sarkozy said that "there are many ideas" for further sanctions - "on just one condition, that it be the whole of the international community that is convinced of the necessity of sanctions." "That is where the problem is," he said. "It is on that front that Ms. Merkel and I are going to work a lot." Merkel's government said earlier Monday that officials from the six countries trying to address concerns about Iran's nuclear program - the US, France, Britain, Russia, China and Germany - would meet near Frankfurt on Wednesday. It said the meeting would involve political directors - foreign ministry officials below ministerial level. The French Foreign Ministry said the gathering would prepare for a meeting later in September on the Iran nuclear issue, which will take place on the sidelines of the United Nations General Assembly in New York. In its latest report, the International Atomic Energy Agency said it has pressed Iran to clarify the purpose of its uranium enrichment activities and reassure the world that it's not trying to build an atomic weapon. The agency acknowledged that Iran has been producing nuclear fuel at a slower rate and allowed U.N. inspectors broader access to its main nuclear complex in the southern city of Natanz and to a reactor in Arak. But the agency said "Iran has not suspended its enrichment-related activities." Iran insists its nuclear program is geared solely toward generating electricity. Sarkozy said he backs Obama's efforts to reach out to Iran. However, "this hand cannot remain outstretched indefinitely to leaders who do not respond," he said.