president, I had been working to my limits both physically and mentally until the July Upper House election," he said. "But I think I was very tired, which made me lose vigor for a moment when I invited the confusion (over the proposed grand coalition)."

Ozawa has had a history of heart problems.

His decision to stay at the helm is expected to quell the DPJ's internal strife for now, but the bizarre event has had a negative impact on the party at a time when the opposition is preparing to capitalize on a rare but realistic chance of edging the LDP-led ruling bloc should a general election be called.

Ozawa said that despite the opposition's decisive victory in the Upper House election in July, in which the ruling bloc lost its control of the chamber, a Lower House election would be much more challenging.