White House national security spokesperson John Kirby said the talks were part of "a routine, continuing dialogue," Reuters reported.
The department said in a statement on Friday that Washington hosted the meeting on June 13-14 in Cairo among the five nuclear weapons states, describing it as "an ongoing exchange in the context of the Nuclear Non-Proliferation Treaty (NPT)."
The experts were drawn from the countries' respective ministries of foreign affairs and defense, the department said. They "discussed strategic risk reduction, as well as nuclear doctrines and policy," it added.
The NPT, which took effect in 1970, aims to halt the spread of nuclear weapons-making capability and guarantee the right of members to develop nuclear energy for peace means.
The treaty allowed the five nuclear weapons states - who are the permanent members of the United Nations Security Council - to keep their nuclear arsenals.
A State Department spokesperson said expert representatives had also met in Dubai in February as part of the dialogue under the NPT, which the United States is currently chairing.
"We found both multilateral conversations to be professional and useful," the spokesperson said in an emailed response that did not address the question of whether any bilateral talks took place.