Japan and Mexico are still unable to agree on several key issues in negotiations for a free-trade agreement, a senior Japanese trade official said Monday.

"Both countries assume now that we have entered the final stage of negotiations, but we still have seen a seesaw over several core issues," Seiji Murata, vice minister of economy, trade and industry, told a news conference.

The core issues are believed to include farm and industrial products. He said Japan and Mexico have narrowed their differences over most of the other issues through working-level negotiations.

Senior Mexican officials, including Angel Villalobos, vice minister for economy and international commerce, visited Tokyo over the weekend. Murata said this demonstrates Mexico is serious about the negotiations.

Japan and Mexico are trying to complete the bargaining by the end of this month, a deadline proposed by Mexico. The two countries have continued working-level talks that started Wednesday in Tokyo.

It is expected the talks will be upgraded to the vice-ministerial level, perhaps later this week, if deemed necessary to further bridge the gap over contentious issues.

The two countries had planned to seal an FTA during President Vicente Fox's visit to Japan in October but missed the target mainly due to Japan's reluctance to open up its farm market.