Japan and the United States have agreed to open formal negotiations on concluding a long-awaited social welfare pact aimed at preventing double collection of public pension premiums from their citizens, government sources said Thursday.

The agreement was finally reached after years of an informal dialogue between the two governments on their public pension systems, the sources said.

They said that the first round of formal negotiations on the social welfare pact will be held as early as this summer, although a specific date has not yet been fixed.