Thai opposition parties are crying foul over a visit to Japan by fugitive former Prime Minister Thaksin Shinawatra whose sister recently won a national election. Thaksin is on a routine and personal visit to Japan, his aides said. The multi-millionaire spends most of his time in self-exile in Dubai. Thaksin, 61, was ousted in a military coup in 2006 and soon after received a 2-year prison sentence for tax fraud. He fled in 2008 rather than serve his sentence, leaving an estimated $2 billion in frozen assets. Thaksin arrived in Japan Monday -- his first visit for three years -- for a weeklong stay and he reportedly intends to travel to areas hit by the March tsunami and earthquake disaster, a report in the Bangkok Post said. \"I\'m very happy that I\'ve come to Japan again,\" he said on his arrival. But the leader of Thailand\'s Democrat party, Abhisit Vejjajiva, claimed Thailand\'s Foreign Minister Surapong Tovichakchaikul intervened to help arrange a Japanese visa for Thaksin. Abhisit said the Japanese government had confirmed Bangkok had requested Japan issue an entry visa to Thaksin and that the Japanese government said last week it granted a special permit for Thaksin to enter the country at the behest of the Thai government. But Surapong, who denies he helped Thaksin, hit back at Abhisit, saying he will file a claim for defamation of character. The war of words between the parties is expected to continue for months if not years because of the close connection between Thaksin and his younger sister who roundly defeated Abhisit in a July election. The Democrat Party was crushed by its main rival the Pheu Thai Party, led by the neophyte politician Yingluck Shinawatra, 44. Abhisit, who lost his own seat in Parliament, said immediately after the defeat he will step down as soon as the party has a leadership voterace, expected by early October. Yingluck, who earned a master\'s degree in political science from Kentucky State University in 1990 and is a successful businesswoman, had little political experience. Even so, she managed to bolster her already large number of seats in Parliament with the coalition announcement, raising the number of government seats to 299 out of 500. But critics of Yingluck -- Thailand\'s first female prime minister -- say real government power lies in Dubai with her brother. In the event of a divisive issue, her government could prove fragile because it\'s a six-party coalition. What is likely not to be swept easily under the carpet is her relationship with her brother. Thaksin also is wanted by police for questioning about major street protests that crippled parts of central Bangkok last year from February to May. The demonstrations left 90 people dead and some 2,000 injured. He denies all accusations that he helped organize the demonstrations and has said he called for peace by the protesters during the demonstrations.