SEOUL, South Korea — South Korea and the Obama administration delayed the deadline for a deal that Seoul had hoped would allow it to begin making its own fuel for its civil nuclear energy program, but that the United States feared would undermine its attempts to curb nuclear proliferation.

It had appeared that a deal might be reached this year, but officials in both countries said the deadline would slip until 2016.

The government of President Park Geun-hye has been pushing hard for the United States to lift a ban, part of a treaty signed in 1972, that prevents South Korea from enriching uranium and reprocessing spent nuclear fuel.

But the same technologies are also used to make material for nuclear weapons. American officials have said that lifting the ban would have complicated diplomatic efforts to persuade North Korea to give up its nuclear programs and to stop any attempt by Iran to develop atomic weapons.