By Farhad Pouladi
The sources confirmed the participation of Pakistani President Asif Ali Zardari and Afghanistan's Hamid Karzai in the summit, which will discuss the rebuilding of war-shattered Afghanistan.
The meeting had been expected to go ahead on May 19 but was postponed due to the heavy programme of Zardari.
Iran's ambassador to Islamabad, Mashallah Shakeri, was quoted Friday on the website of Iranian state-run television as saying Zardari would arrive in Tehran on Saturday to take part in the following day's summit.
His comments were confirmed in Islamabad by Pakistani foreign office spokesman Abdul Basit.
"President Zardari is going to Iran. He will attend the summit in Tehran on May 24," Basit said.
Afghanistan's ambassador to Tehran, Mohammad Yahya Ma'aroufi, Friday confirmed Karzai's participation.
"President Hamid Karzai will arrive in Tehran on Sunday May 24 to take part in the meeting," the ambassador told AFP.
Iranian foreign ministry spokesman Hassan Ghashghavi said that the summit would be held in Tehran at "the beginning of the coming week," without specifying the day. Saturday is the beginning of the week in Iran.
The Tehran talks are expected to discuss efforts to rebuild Iran's eastern neighbour which is battling a resurgent Taliban insurgency and also to explore ways to rein in the rising violence in Pakistan.
Ahmadinejad, Karzai and Zardari met less than three months ago in the Iranian capital Tehran for a regional economic summit, along with leaders of other neighbouring states.
That summit pledged to help rebuild Afghanistan, and also the Gaza Strip after Israel's devastating offensive at the turn of the year.
The administration of US President Barack Obama has been working towards engaging Tehran in efforts to rebuild Afghanistan.
Iran had also attended a US-backed international conference on Afghanistan in The Hague on March 31.
Engaging Iran is part of Obama's strategy to secure the help of all Afghanistan's neighbours in reconstructing the Muslim country.
Iran has not had diplomatic relations with the US for nearly three decades, and was included in former president George W. Bush's so-called "axis of evil" along with North Korea and Iraq.
Despite their rivalry, Washington and Tehran are both sworn enemies of the Taliban, a extremist Sunni Muslim militia initially backed by Pakistan, that ruled Afghanistan from 1996 to 2001.
Shiite Iran, which has close ethnic and religious ties with Afghanistan, has long suffered from the effects of opium production in its eastern neighbour, with easily available heroin fuelling a big rise in drug use at home.
Afghanistan is the source of 90 percent of the world's heroin.
