The shrine, in the centre of Tokyo, honours 2.5 million soldiers, including 14 convicted by a 1948 war crimes tribunal, and is viewed by much of the rest of Asia as a symbol of Japan's militarism. Two weeks ago a Japanese court ruled that Mr Koizumi's visits violated the country's constitution.
Mr Koizumi's fifth shrine visit since he came to power in 2001 sparked outrage yesterday in Beijing, Hong Kong and Seoul and led to the cancellation of several meetings, including a visit to China by the Japanese Foreign Minister, Nobutaka Machimura.
The South Korean Foreign Minister, Ban Ki-Moon, told the Japanese ambassador to Seoul that Mr Koizumi's insistence on visiting Yasukuni was the "greatest obstacle" to formal ties, before warning that President Roh Moo-Hyun's trip to Tokyo in December may be scrapped.
The Chinese ambassador to Japan, Wang Yi, said the visit had "deeply hurt the feelings of people in countries that suffered during the Second World War" and called it a "serious provocation", coming at the same time as the "glorious return" of the space mission, Shenzhou 6.
Dozens of online bulletin boards in China alleged that Mr Koizumi deliberately timed his trip to steal Beijing's thunder, but the visit on the opening of the shrine's autumn season had been predicted in Japan, as had the likely reaction from Beijing and Seoul.
China is likely to be further angered by an unwelcome intervention by the former Taiwan president, Lee Teng-hui, who said at the weekend that he supports the Yasukuni visits.
Mr Koizumi, who was returned to power in last month's general election with a huge majority, seems to have calculated that he can ride out the diplomatic storm by insisting that the visits are private.
"I went as an individual citizen and not as ... Prime Minister," he said, adding that "mourning the war dead once every year is a good thing". However, in one of several Yasukuni-related lawsuits, the High Court in Osaka has ruled that the visits violate the separation of state and religion, a ruling the Prime Minister called "strange". "Every country should be able to respect its war dead," he said.
Mr Koizumi has pledged to visit the shrine on the most explosive date of all - 15 August, when Japan commemorates the end of the Pacific war - and many of his supporters expect him to do so before he steps down from office next year.Reuse content