Restarting cooling to the spent fuel pool at reactor 4 had been of particular urgency for Tepco as it had the highest number of fuel assemblies stored there, Kyodo news agency reported.

BBC: Power at Fukushima nuclear fuel ponds restored

This is a very difficult situation, and there will be a lot of work continuing as we go forward to deal with continuing to cool the reactors and to provide cooling to the spent fuel pool.

WHITEHOUSE: Press Briefing

The IAEA statement was released hours after Tepco temporarily shut down the cooling system in the second unit's spent fuel pool following the discovery of dead rodents near a transformer.

BBC: IAEA calls for improvements at Japan's Fukushima plant