Japan has proposed during negotiations with the United States to slash its 38.5 percent tariff in imported beef to 9 percent over 15 years under an envisioned Pacific Rim free trade deal, negotiation sources said Thursday.

Tokyo also called for a safeguard measure that allows it to raise tariffs back to 20 percent if U.S. beef imports surge under the Trans-Pacific Partnership initiative, the sources said.

Japan offered the concession in response to strident calls from the United States to open its agricultural market. If the two sides can settle the issue, it will provide crucial momentum for concluding the broader 12-country negotiations.