TOKYO, Dec. 20 (Xinhua) -- The yen weakened to a roughly one-month low in the 157 range per dollar late Friday, nearing levels that could trigger official buying, after the Bank of Japan (BOJ) raised benchmark interest rates without offering clear plans for future hikes.

The yen fell sharply against the dollar on Friday following the BOJ's widely expected move of raising its policy rate to 0.75 percent, its highest level in three decades.

The yen's losses extended after BOJ Governor Kazuo Ueda offered little clarity on the timing and pace of future rate hikes at a post-meeting news conference.

The dollar rose as high as 157.67 yen on the day, hitting its high level in a month and set for its largest one-day rise since early October, according to Reuters.

Japanese authorities will "respond properly" if the yen shows excessive movement in the foreign exchange market, Finance Minister Satsuki Katayama said late Friday.

With trading likely to be thin in the coming week due to the Christmas holidays, volatility in the yen could pick up, analysts warned.

"Intervention risks over the quieter Christmas period are becoming a more realistic prospect," the Nikkei Asia reported, citing Derek Halpenny, an analyst at the Japanese bank MUFG. ■