Prime Minister Naoto Kan denied Tuesday that his visit to the Fukushima No. 1 nuclear plant on March 12, the day after the killer earthquake and tsunami hit the Tohoku region, delayed a crucial step to avert an atomic crisis.

Just after midnight on March 12, pressure in the No. 1 reactor rose to an extremely high level. To release the pressure and prevent an explosion, Tokyo Electric Power Co. needed to open the valves and release radiation-polluted gas.

But Tepco didn't start the ventilation process until 9:04 a.m. and pressure didn't lower until 2:30 p.m. Then at 3:36 p.m., a hydrogen blast blew up the No. 1 reactor building. Kan arrived at the plant by helicopter at 7:11 a.m. and stayed for an hour.

Media reports said the ventilation was delayed until 9 a.m. because Kan flew in by helicopter. The government claims it has been pushing Tepco repeatedly to hurry with the ventilation, but the lack of electricity delayed the process.

"It is not true that the visit delayed" the reactor's ventilation to release pressure, Kan told an Upper House Budget Committee session Tuesday.

Kan said he believed it was important to grasp what was happening at the scene. "Getting briefed from the person in charge and meeting him in person was very effective in mapping out a plan later."