U.S. Deputy Secretary of State Robert Zoellick said Monday it was "an unacceptable mistake" that a shipment of U.S. beef that arrived in Japan contained bone parts in violation of an accord on preventing mad cow disease, prompting Tokyo to once again ban American beef.

In a meeting with Chief Cabinet Secretary Shinzo Abe, Zoellick expressed "profound regret for this failure," a Foreign Ministry official said in briefing reporters.

After meeting with Zoellick, Abe told reporters the U.S. needs to report the results of its investigation and take measures to prevent a recurrence if it wants Japan to lift the ban again.

"Japan values food safety above everything else," Abe said. "If concerns over U.S. beef are not swept away, consumers will never buy U.S. beef."

Japan announced Friday it was reimposing the ban on U.S. beef imports after inspectors found spinal cord material in a recent shipment. Spinal cords are among beef parts not allowed under an agreement reached late last year for lifting the ban.

The announcement came a month after a two-year-old ban on U.S. beef was lifted.

Abe meanwhile said he instructed ministries to have Japanese importers voluntarily inspect and report whether other bone materials have been found since U.S. beef imports were resumed.

Zoellick said the New York meatpacker that shipped the spinal cords was removed from the list of those allowed to export to Japan, the Foreign Ministry official said.

He added that Washington is doing its utmost to find out how and why the spinal cords were shipped to Japan, and to map out ways to prevent a recurrence, the official said.

Zoellick also met with Prime Minister Junichiro Koizumi and Foreign Minister Taro Aso. On other issues, Zoellick asked Abe and Aso how Japan sees its current relationship with China -- a remark that reflects concerns of the Bush administration over the dispute stemming from Koizumi's repeated visits to Yasukuni Shrine.