Amnesty International has sent a letter to Justice Minister Jinen Nagase expressing "grave concern" over the executions of four inmates Dec. 25, the international human rights group said.
"The retrograde step runs counter to the universal protection of human rights and is at odds with the international trend away from the use of the death penalty," Amnesty said in the letter issued in the name of its secretary general, Irene Khan.
It said that its provisional figures indicate only 20 of the 193 U.N. member states carried out state killings in 2006 and that the latest executions in Japan "will send a discouraging signal to nations in the Asia-Pacific region at a time when others -- South Korea and Taiwan, for example -- are considering the abolition of the death penalty."