Moscow on Monday said it had sent "instructors" to Sudan, where demonstrators have been protesting against President Omar al-Bashir for weeks, following reports of sightings of Russian-speaking soldiers in Khartoum.
Kremlin spokesman Dmitry Peskov did not specify who the "instructors" were, but said they were in Sudan "absolutely legitimately".
"There are really instructors there, they have been working for some time, a considerable time," Peskov told journalists.
"This is in the framework of Russia-Sudan bilateral relations, absolutely legitimately."
"Of course our instructors are in Sudan," Deputy Foreign Minister Mikhail Bogdanov said, Interfax reported.
"There are both private and state instructors" who have been asked to "help with preparing personnel", Bogdanov said.
Russian foreign ministry spokeswoman Maria Zakharova last week said "representatives of private security firms" were working in Sudan but had "nothing to do with Russia's government structures".
She said they were training personnel for Sudan's "institutions of force", which could refer to law enforcement or military.
Russian President Vladimir Putin met Sudan's al-Bashir last July in Moscow where the Sudanese leader said Russia was playing an important role in "preparing Sudanese military personnel" in the framework of bilateral cooperation.
Opposition to al-Bashir, who has been in power for about three decades, has in recent weeks grown into nationwide rallies, with dozens dead in violence and a massive deployment of riot police.
British newspaper The Times said that Russian mercenaries in Sudan were part of the so-called Wagner private security group, a mercurial company sending soldiers to a number of conflicts overseas.
Russian reports alleged in late 2018 that dozens of Wagner mercenaries were in the country.
The secretive group has also been active in the Central African Republic, according to reports.
Last year three Russian journalists investigating its activities in the country were murdered.
Russian officials have labelled the crime a violent robbery.