Asked whether Japan's authorities should consider widening the exclusion zone, a senior IAEA official said: "There should be a consideration about this." The official requested anonymity.
At the same time, IAEA officials said radiation rates are declining and levels are not unhealthy in dozens of Japanese cities including Tokyo, for which the Vienna-based agency is receiving official Japanese data.
On Sunday, one measurement 58 km from Fukushima registered 5.7 microsieverts per hour, the IAEA said in data provided to reporters.
At that rate, people would be exposed to the IAEA's annual recommended maximum radiation of one millisievert within about seven days.
The IAEA assumes that receiving more than one millisieverts per year, in addition to the dose from naturally occurring radiation, raises long-term cancer risk.
IAEA radiation expert Gerhard Proehl also mentioned one site more than 30 km from the nuclear plant where 100 microsieverts per hour are being measured.
Authorities have evacuated people living within 20 km of Fukushima's six reactors, and have told people within 30 km to stay indoors.
In addition, the IAEA said it seeks more information about radioactivity across Japan. So far, above-limit doses have been found in vegetables and milk in several regions around Fukushima.
Agency experts said some residual radioactivity would remain in the areas for years, but most of it would decline rapidly because the radioactive iodine isotopes have a short half-life and decay quickly.
The radiation comes from two explosions and possibly from a fire at Fukushima, which have occurred in the days after the plant was hit by an earthquake and tsunami March 11.
Radioactivity occurs when an atom's nucleus disintegrates into so-called isotopes that can enter the soil or the food chain. These isotopes emit potentially harmful radiation. Sieverts are the unit for measuring the radiation dose for humans.
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