Russian President Vladimir Putin approved the ban from January 1 as part of a law passed to retaliate against U.S. legislation intended to punish Russian human rights abusers.
Moscow had told Washington it was also terminating a bilateral agreement regulating adoptions - but Putin's spokesman on Thursday said a technicality meant that agreement would have to remain in force until the beginning of 2014.
"The agreement is still in effect," Dmitry Peskov told state-run news agency RIA, citing a built-in one-year delay to any terminations.
He confirmed that to Reuters, and said it would be up to legal experts to determine what effect it might have on American families who were still going through the process of adopting Russian children when the ban was imposed.
The U.S. State Department said it was unclear about the impact of Peskov's statement but told reporters it was "very hopeful" it would be able to work through adoption cases that had already begun.
U.S. officials were sifting through emails from about 950 American families to establish where they were in the adoption process, said State Department spokeswoman Victoria Nuland.
A prominent Russian defence lawyer, Genri Reznik, told Ekho Moskvy radio station that because an article of the Russian constitution says international treaties take precedence over Russian laws if they contradict one another, Peskov's announcement meant adoption procedures could continue for a year.
UNCERTAINTY
But Peskov added to the uncertainty in later interviews by suggesting only children whose adoptions have been approved by Russian courts would be able to go to the United States.
"In cases where certain legal procedures have not been completed, a full ban on adoptions by parents from America takes effect," Peskov told the Internet and cable TV channel Dozhd.
"The (Russia-U.S.) agreement is in no way a mechanism that obliges the Russian side to give its children up for adoption," he added.
Peskov gave no numbers on Thursday, but he was quoted as saying in late December that six adoptions that had been approved would go through while another 46 that were underway would not. He was not immediately available to make further comment on Thursday.
Russian lawmakers have said the adoption ban was justified by the deaths of 19 Russian-born children adopted by American parents in the past decade.
But child rights activists have accused the Russian government of making vulnerable children pawns in a political dispute. Opponents of Putin are planning a protest march over the law in Moscow on Sunday.
Critics of the ban say Russian orphanages are overcrowded and that the number of adoptions by Russian families remain modest. Americans have adopted more than 60,000 Russian children since the 1991 Soviet collapse, including 962 in 2011.
(Writing by Steve Gutterman; Editing by Andrew Heavens)