Ahmadinejad attended a global summit on food at the UN Food and Agriculture Organization's Rome headquarters in early June.
"On the eve of the [Iranian] president's visit to Rome, we checked the radiation levels in his temporary residence," Abolfazi Zohrevand told Iran's IRNA news agency.
"We found out that the radiation was higher than normal and its intensity was rapidly increasing," he said, adding that several devices were used to avoid potential error in readings, but they all showed the same results.
Earlier, Ahmadinejad himself mentioned another assassination attempt during his March visit to Baghdad and said only changes to his schedule had foiled the plot. However, the West and even some inner Iranian circles dismissed his allegations.
The Iranian president pledged last week to provide proof that the United States was behind an attempt on his life in Iraq.
Ahmadinejad, 51, who became president in 2005, is a strong critic of the West and has also called for Israel "to be wiped off the map," while Washington considers Iran to be the world's leading state sponsor of terrorism.