BERLIN (AFP) - Russian Foreign Minister Sergei Lavrov said on Tuesday that his US counterpart John Kerry had acknowledged problems in cases of US-adopted Russian orphans and promised "full transparency".

The issue of adoptions of Russian orphans by US nationals has become a major sticking point in bilateral ties and has triggered an unprecedented standoff in recent weeks.

"We discussed problems with adoptions of Russian children in detail," mr Lavrov was quoted as saying by Russian news agencies.

"John Kerry acknowledged that these problems are not made up, that they are real and assured (us) that he will personally take all necessary measures to ensure full transparency for us and accountability in this sphere in the United States."

"I believe that this is a very important statement," Mr Lavrov was quoted as telling reporters after his closely-watched meeting with America's top diplomat.

"We will make sure that these words are translated into practical deeds," Mr Lavrov said.

The trigger for the standoff was the passing by the United States late last year of a bill targeting Russian officials with sanctions over the prison death of Russian lawyer Sergei Magnitsky.

Russia retaliated with a ban on all US adoptions, saying Russian children in the United States were abused and even murdered by their adoptive parents.

Russian officials have blamed US authorities for failing to prosecute US parents who harm Russian adoptees, justifying the adoption ban.

Last week, the State Duma, Russian parliament's lower house, adopted a special appeal to the US Congress asking American lawmakers for help in returning the brother of a young boy who died in Texas last month.

The US ambassador to Moscow Michael McFaul called on Russian officials to stop "sensational exploitation" of the tragic death.