The trip was planned well in advance of the conflict in Georgia, which -- bordering as it does on Turkey and separated from Iran only by small landlocked Armenia -- is a geopolitical concern for both nations.

Ahmadinejad, who arrives Thursday in Istanbul, will meet in the metropolis with President Abdullah Gul and Prime Minister Recep Tayyip Erdogan, said the official, who requested anonymity and gave no details.

Israel last week voiced misgivings over Ahmadinejad's visit, saying it was "not the appropriate time" for Turkey, its main regional ally, to host the Iranian president.

"It is not a good idea to give legitimacy" to a leader who has called for the destruction of Israel and denies the Holocaust, moreover at a time when Western powers are mulling fresh sanctions against Iran over its controversial nuclear programme, an Israeli diplomat based in Ankara said.

Ankara, which had in the past complained of Iranian attempts to undermine Turkey's secular order, has in recent years significantly improved relations with its eastern neighbour.

A NATO member and a candidate for EU membership, Turkey argues that its close dialogue both with the West and Tehran could be an asset for a peaceful solution of the international standoff over Iran's nuclear programme.

Foreign Minister Ali Babacan said last month that the six world powers trying to negotiate a deal with Iran over the nuclear issue have both asked for Turkish help.

Even though Turkey has no formal mediation mission, it has undertaken a role of "consolidating and facilitating" the negotiations, he said.

Turkey says Iran -- which is defying UN Security Council demands to halt uranium enrichment -- has the right to possess nuclear power for peaceful purposes, but it opposes nuclear weapons in the region.

The non-Arab secular country has been Israel's main regional ally since 1996 when the two signed a military cooperation accord -- much to the anger of Arab countries and Iran.

Turkey is also mediating indirect talks between Israel and Syria.

Turkish news media say Ahmadinejad will be hosted in Istanbul because protocol in the capital Ankara would have required him to visit the tomb of Turkey's secularist founder Mustafa Kemal Ataturk, which the head of the Islamic state is reportedly reluctant to do.

Turkey has stepped up cooperation with Iran against separatist Kurdish rebels active in both countries, and in 2001 began buying Iranian gas via a pipeline between the two countries, overriding US discontent.

Turkey's interest in Georgia is heightened by another pipeline that carries crude oil from the Caspian Sea from Azerbaijan's capital Baku via Tbilisi to Turkey's Mediterranean port of Ceyhan.

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