TOKYO (AP) — Japan's top nuclear regulator has raised safety concerns about hastily built storage tanks and their foundations amid reports of new leaks of radiation-contaminated water.

Nuclear Regulation Authority Chairman Shunichi Tanaka said Monday that a small leak and signs of possible leaks have been spotted at several other Fukushima Dai-ichi storage tanks. Officials say part of the leak has escaped into the sea.

He said the discoveries were the result of closer inspections after a 300-ton leak two weeks ago. Tanaka raised concerns about the tanks' foundations and urged careful monitoring.

The plant's operator says it suspects other possible leaks because radioactivity has been detected near the tanks, although it is not considered deadly.

The latest leaks have triggered further concerns about the plant's ability to manage the contaminated water.