Japanese and U.S. negotiators narrowed their differences but were still unable to close a deal as the sixth round of official bilateral civil aviation talks ended here Thursday.

Officials were aiming to draw up a four-year transitional agreement during the four-day meeting, to increase aviation services for the trans-Pacific market. "We could not reach a final agreement," a senior official in the Japanese transport ministry said. "But this was the most productive meeting that we have had. We will stay in contact on an unofficial basis to reach a final agreement at the next meeting." The two sides will meet again from Jan. 20 to 22 in Washington.

"The U.S. has started to show a considerably more flexible attitude. It remains unknown how the next meeting will end up because we are still at odds over some issues, but we are moving toward an agreement," the official said. Negotiators are closing the gap over such key issues as code-sharing and beyond rights, which allow a carrier to fly to a third country via Japan or the U.S.