Mr Fukuda, facing dwindling approval ratings, suddenly quit on Monday. His Liberal Democratic Party (LDP) is reportedly set to meet on September 22 to choose his successor.

Japan had been hoping to arrange the first-of-a-kind three-nation summit on September 21 in the western city of Kobe.

'I'm afraid the schedule of the summit will be affected somehow,' said Foreign Minister Masahiko Komura.

'I don't think that delaying the meeting would negatively affect diplomatic relations,' he told reporters. 'But I want to make arrangements so that the meeting will not be cancelled.'

Mr Fukuda is known for his efforts to repair relations with other Asian nations which have been tense due to the legacy of Japanese imperialism.

Earlier this year he reached a breakthrough agreement with Beijing to share disputed natural gas resources in the East China Sea.

But South Korea had not publicly committed to attending the summit due to a renewed dispute with Japan over control of a small set of islands.

Japan had tense relations with China and South Korea during the 2001-2006 premiership of Mr Junichiro Koizumi, who each year visited a shrine venerating Japanese war dead including war criminals. -- AFP