"We are now working with her lawyer. He is working with her family, with our embassy," Lavrov said at his annual press conference.
German police urge calm as teen rape claim sparks online storm
"It is clear that the girl - absolutely for sure not voluntarily - disappeared for 30 hours," Lavrov added.
Berlin police last week rejected a claim by a 13-year-old German-Russian teenager, identified as "Liza" by Russian media, that she had been kidnapped and raped by foreigners.
The girl had gone missing in Berlin, reportedly on her way to school, on January 11.
She subsequently returned and filed a police report, with her parents telling investigators she was kidnapped by three men at a railway station in eastern Berlin.
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The girl described the men as coming from "southern countries and speaking broken German", saying they drove her to an apartment where they raped and beat her, according to German media reports.
The case has sparked outrage and allegations on far-right and Russian media of an official cover-up.
The case has prompted parallels with German police's initial silence over a spate of sex assaults on New Year's in Cologne that women said were carried out mainly by Arab and North African men.
Germany took in nearly 1.1 million asylum seekers last year, mainly from Syria, Afghanistan and Iraq, and pressure has been mounting on Chancellor Angela Merkel over her welcoming stance toward refugees fleeing war.
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Lavrov said he regretted the news of Liza's disappearance had "been hidden for a very long time for some reason."
Russian state media outlets have also rejected the German police findings, calling them an attempt to cover up the crime.
Pro-Kremlin NTV channel went as far as to claim that "in Germany and in Sweden, residents are regularly raped by refugees.
"There are several cases of sexual assault but the local authorities and police hide these facts and do not open criminal investigations," it said.
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