(Corrects date of China protest in paragraph 5)
TOKYO, April 21 (Reuters) - Japanese Prime Minister Shinzo Abe has sent a ritual offering to the Yasukuni Shrine, seen by critics as a symbol of Japan's past militarism, media reported on Monday, a move likely to further strain ties with China and South Korea.
The offering from Abe, who visited the shrine in December, was sent just before U.S. President Barack Obama's three-day visit to Japan, which begins on Wednesday.
Japanese media said Abe would not visit the shrine in person. Fourteen Japanese leaders convicted as war criminals by an Allied tribunal after World War Two are honoured there, along with Japan's war dead.
Abe's visit to the shrine in December infuriated China and South Korea. It also prompted the United States, Japan's closest ally, to express its disappointment.
China protested on April 12 after internal affairs minister Yoshitaka Shindo visited the shrine. Keiji Furuya, another cabinet minister, has also paid his respects. A number of lawmakers are also expected to visit the shrine during its spring festival this week.
Tensions with China were likely to increase further after a Chinese maritime court on Saturday seized a ship owned by Japanese shipping firm Mitsui O.S.K. Lines, saying the company had failed to pay compensation stemming from a wartime contractual obligation, Kyodo news agency said.
It appeared to be the first time an asset of a Japanese company had been seized in a lawsuit concerning wartime compensation.
Visits by Japanese leaders to the Tokyo shrine have outraged China and South Korea, which suffered under Japanese occupation and colonisation in the 20th century. Beijing and Seoul have been highly critical of previous offerings made by Abe.
Abe has said that, like predecessors such as former premier Yasuhiro Nakasone who visited the shrine, he had high regard for Japan's ties with China and South Korea.
In March, Obama brought together Abe and South Korean President Park Geun-hye for their first face-to-face talks to help Washington's two key Asian allies mend ties. (Reporting by Dominic Lau and Edmund Klamann; Writing by Linda Sieg and Elaine Lies; Editing by Paul Tait)