VIENNA (AFP) - The UN atomic watchdog Sunday noted "some positive developments" at Japan's stricken Fukushima nuclear power plant over the past 24 hours, but warned that the crisis there remained serious. "There have been some positive developments in last 24 hours, but the overall situation at the Fukushima Daiichi nuclear power plant remains very serious," Graham Andrew, a scientific and technical advisor to the head of the International Atomic Energy Agency, told a regular daily press briefing here. Efforts to restore electrical power to the reactor cooling systems on the site were continuing in "difficult conditions," Andrew said. Following an initial rise in pressure in the pressure vessel of unit 3, plans were made to vent it to avoid a possible explosion. "However, from information recently received from NISA (the Nuclear and Industrial Safety Agency), they have decided not to vent as the vessel pressure has started to reduce, which is good news," the expert said. The situation in the reactor's spent fuel ponds was "relatively stable but is still of concern," Andrew said. The IAEA still lacks data on water levels and temperatures at the spent fuel ponds at units 1, 2, 3 and 4.