WASHINGTON — A long-lasting radioactive element has been measured at levels that pose a long-term danger at one spot 25 miles from the crippled Fukushima Daiichi nuclear power plant, raising questions about whether Japan’s evacuation zone should be expanded and whether the land might need to be abandoned.

The isotope, cesium 137, was measured in one village by the International Atomic Energy Agency at a level exceeding the standard that the Soviet Union used as a gauge to recommend abandoning land surrounding the Chernobyl reactor, and at another location not precisely identified by the agency at more than double the Soviet standard.

The measurements, reported Wednesday, would not be high enough to cause acute radiation illness, but far exceed standards for the general public designed to cut the risks of cancer.

While the amount measured would not pose an immediate danger, the annual dose would be too high to allow people to keep living there, according to Edwin Lyman, a senior scientist at the Union of Concerned Scientists, an American organization that is often critical of nuclear safety rules. Cesium persists in the environment for centuries, losing half its strength every 30 years.