Smoothing strained ties with Japan is just one challenge facing Barack Obama as he embarks on his first Asian tour as US President.Japan’s new Prime Minister Yukio Hatoyama wants a diplomatic course less dependent on long-time ally Washington. But both leaders vowed to revitalise their countries’ five-decade security alliance. “Both Yukio and I were elected on a promise of change but there should be no doubt as we move our nations in a new direction, our alliance will endure and our efforts will be focused on revitalising that friendship so that it is even stronger and more successful in meeting the challenges of the 21st century,” Obama told a joint news conference in Tokyo. As well as a row over a US military base in Japan, there have been protests there over the American leader’s failure to visit Hiroshima and Nagasaki during his trip. Environmental demonstrators meanwhile appealed to Obama and his host to lead the world on climate change.