The announcement followed the president's two-day visit to Azerbaijan, where President Ilkham Aliyev accepted an invitation to the summit. The other three Caspian littoral states are Kazakhstan, Russia and Turkmenistan.
The Tehran Times newspaper earlier reported that Ahmadinejad, who has visited ex-Soviet countries Kyrgyzstan and Turkmenistan in the past week, had also invited Russian President Vladimir Putin to the summit. The Iranian leader met with Putin in Kyrgyz capital Bishkek at an August 16 summit of the Shanghai Cooperation Organization (SCO), in which Iran has observer status.
On June 20, Caspian foreign ministers convened in Iran's capital to discuss a draft declaration on the Caspian Sea, expected to be adopted at the upcoming summit.
The Caspian Sea's status has long been under discussion among the five littoral states, which have yet to divide the sea's substantial reserves, including oil, natural gas, and fish, in particular caviar-bearing sturgeon.
The first summit of Caspian nations took place in 2002. It was decided at the time to hold the second the following year, but the meeting was repeatedly put off.
The 2002 summit in Ashgabat, Turkmenistan addressed the legal rights of Caspian nations to explore the huge oil reserves beneath the world's largest saline lake.