Farm minister Yoshinobu Shimamura urged a government panel Friday to draw a conclusion quickly on whether to terminate the blanket testing for mad cow disease, in order to lift Japan's 14-month-old import ban on U.S. beef.

"If they only hold discussions once in three weeks, it will take till early May. The U.S. side doubts whether we are handling the matter seriously," Shimamura told a press conference.

His remarks followed news reports that 20 U.S. senators sent a letter dated Feb. 18 to Japan, threatening to pursue retaliatory economic actions if it fails to quickly lift the ban.