After a hiatus of about six months, Japan and Mexico will resume tough negotiations next week on concluding a pact aimed at shoring up the flow of investment across the Pacific.

Although some signs of progress have emerged recently in the form of informal contacts, it remains uncertain whether the two countries will be able to conclude an agreement by December, as Mexico desires.

Government sources said Thursday that senior Japanese and Mexican officials will hold a fresh round of negotiations on the investment pact on Sept. 28 and Sept. 29 in Tokyo, and that Mexico has indicated a willingness to grant Japanese companies already in the country the same privileges its U.S., Canadian and European Union rivals enjoy.