Officials said they were investigating whether the poisoning was intentional.
An official with the environment ministry said 11 policemen had died.
However, the governor of Wasit province - where the poisoning took place - denied any deaths, though he said some of the victims were in a critical condition.
There was no immediate explanation for the contradictory reports.
Some of the policemen began bleeding from the ears and nose after the meal, said Jassim al-Atwan, an inspector for the environment ministry, who was liaising in the investigation between the health ministry and the base, located in the town of Numaniya.
"Hundreds of soldiers were poisoned after taking food and water in the iftar," Hamad al-Latif, the governor of Wasit, told the Associated Press, referring to the meal that breaks the sunrise-to-sunset fast during the Islamic holy month. "Investigations are under way to determine the cause."
Samples of the food and water were being tested "to determine the substance in them" and will be sent to Baghdad for further tests, al-Latif said.
Between 600 and 700 policemen were affected to varying degrees, and 11 who had the heaviest amount of the food had died, al-Atwan told AP.
Some of the soldiers collapsed as soon as they stood up from their meal, others fell "one after the other" as they headed out to the yard in the base to line up in formation, al-Atwan said.
Iraqi ambulances and helicopters sent by the US military took the policemen to hospitals in Numaniya and the nearby city of Kut.
The policemen belonged to the 4th division of the National Police, nicknamed the "Karrar" division, after a title of Imam Ali, the fourth Muslim caliph.
The division normally operates around the town of Salman Pak on the southeastern outskirts of Baghdad - an area of intense Shia-Sunni killings. The division had been sent to the base in Numaniya, 80km southeast of the capital, for further training.