The Turkish prime minister has held talks in Tehran with Iranian leaders on bolstering bilateral relations and stabilising the situation in their violence-ridden neighbour Iraq.
During the one-day visit to Tehran, Erdogan also discussed Iraq during talks with supreme leader Ayatollah Ali Khamenei.
"The main aim of this trip is to study the rapid international development, especially the sensitive situation in Iraq, Palestine, Lebanon, and the responsibility that both nations feel in finding a solution," state television quoted Erdogan as saying.
"Iranian and Turkish officials want to extend and boost ties," said Ahmadinejad. "Tehran and Ankara can expand bilateral trade and even jointly invest in other parts of the world together."
US pullout
"Just as in the Vietnam war, the US troops will be pulled out in disgrace." Ayatollah Ali Khamenei, Iran supreme leader Send us your views
"Just as in the Vietnam war, the US troops will be pulled out in disgrace." Ayatollah Ali Khamenei, Iran supreme leader
Send us your views
Khamenei told Erdogan that US forces must make a quick exit from Iraq, predicting that the longer they stayed in the violence-torn country the deeper they would sink in the "Iraqi quagmire".
"If the current US President [George Bush] does not pull out troops from Iraq the next US president will be forced to do so," he said.
"Just as in the Vietnam war, the US troops will be pulled out in disgrace," he said.
Iran and Turkey share a border, a common interest in stemming the activities of Kurdish fighters operating inside their territories, and concerns about the security situation in Iraq.
But Tehran's relations with Ankara have not always been smooth. Turkey is the closest Muslim ally of the Islamic republic's arch-enemy Israel, and also has a key strategic relationship with Iran's other enemy - the United States.