TOKYO, Aug 26 (Reuters) - Japanese stocks fell to three-week lows on Friday, hit by a fall on Wall Street and as investors stayed cautious before a speech by Federal Reserve Chair Janet Yellen, but companies announcing share buybacks attracted buying.

The Nikkei share average ended 1.2 percent lower at 16,360.71 points, its lowest closing level since August 5.

For the week, the benchmark index dropped 1.1 percent.

The broader Topix dropped 1.3 percent to 1,287.90 and the JPX-Nikkei Index 400 declined 1.3 percent to 11,573.51.

(Reporting by Ayai Tomisawa; Editing by Kim Coghill)