In a message read to a meeting of the 57-nation Organisation of the Islamic Conference (OIC) on Monday, Annan also called on Israel to stop killing Palestinian resistance fighters and said Palestinians must equally halt their attacks.
"Iraq is by no means a failed state," Annan told the gathering of OIC foreign ministers in Istanbul, his message read out by his special envoy on Iraq Lakhdar Brahimi.
"I appeal to you to respond favourably to the interim government's request for support," he added, stressing Iraq's well-educated workforce and abundant energy resources.
Iraq's new government formally takes power on 30 June.
Other OIC speakers including host Turkey said the United Nations should play the lead role in rebuilding Iraq.
The OIC, established in 1969, aspires to speak with a united voice on behalf of the world's 1.3 billion Muslims, who constitute about a fifth of humanity. But it lacks means and institutional framework to put its resolutions into effect.
The conference denounced Israeli policies in the Palestinian territories.
Turkey termed Israel's excessive force as a big mistake that did not serve any end other than further escalating tensions and harming civilians," Turkish President Ahmet Necdet Sezer said in his opening address. However, "we do not disregard its security concerns," he said.
"Iraq is by no means a failed state"
Sezer stressed the need for the OIC countries to reform their economic and political systems, though he made no direct reference to US President George Bush's Broader Middle East Initiative, allegedly aimed at promoting democracy in the Islamic world.
"It is of vital importance that members of the OIC demonstrate the clear will to accelerate the ongoing political, social and economic reforms in order to catch up with the contemporary age," Sezer said.
"However...it is necessary to adopt a realistic and case-by-case approach building on the domestic dynamics and the particularities of each country," he said agreeing with Arab states which accuse Bush of trying to impose alien values on them.