The Japan Bank for International Cooperation (JBIC) is likely to lend about $4bn for a $10bn nuclear plant project in Texas, to be developed by NRG Energy.
The loan would mark Japan's first state financing for an atomic power station abroad.
JBIC corporate planning department head Tadashi Maeda told Bloomberg that the bank will offer the loan, provided the project is guaranteed by the US Government.
NRG Energy plans to add two 1,350MW reactors made by Toshiba Corp in Texas.
The reactors will be built by Nuclear Innovation North America, a joint venture between NRG Energy and Toshiba.
Commercial operations at the plant are expected to begin in 2016 and 2017.