Tokyo stocks close lower as strong yen weighs
Japan's currency -- seen as a safe haven in times of turmoil -- rose against the dollar as US President Donald Trump's son, Donald Jr, released emails showing he had embraced Russia's efforts to support the tycoon's presidential campaign against Hillary Clinton.
It was the latest in a string of claims about Russian collusion and accusations of cover-ups -- fuelling worries about the president's ability to push through his market-friendly economic agenda.
The greenback weakened to 113.43 yen from 113.95 yen in New York. A stronger yen hurts the profitability of Japan's exporters.
"The so-called Russiagate problem has surfaced again," which is weighing on the dollar, Shinichi Yamamoto, a senior strategist at Okasan Securities, told Bloomberg News.
Yellen is expected to update lawmakers on the outlook for the world's biggest economy and the timetable for interest rate increases.
Tokyo's benchmark Nikkei 225 index lost 0.48 percent, or 97.10 points, to finish at 20,098.38, while the Topix index of all first-section issues fell 0.48 percent, or 7.80 points, to 1,619.34.
Automakers were among the decliners, with Toyota slipping 0.60 percent to 6,225 yen and Nissan falling 0.56 percent to 1,148 yen.
Game giant Nintendo slipped 0.11 percent to 36,020 yen while market heavyweight Fast Retailing, Uniqlo's operator, fell 0.92 percent to 36,430 yen.
Financial shares also fell, with lender Mitsubishi UFJ retreating 1.73 percent to 738.4 yen and rival Sumitumo Mitsui Financial Group down 1.09 percent at 4,330 yen.