Russian investigators said on Thursday they had detained the director of a Moscow library specialising in Ukrainian literature and opened a criminal case to establish whether she was guilty of inciting ethnic hatred.
The arrest of 58-year-old Natalya Sharina followed a search of the library which investigators said had uncovered printed material containing "anti-Russian propaganda" and extremist writings by Dmytro Korchinskiy, a Ukrainian nationalist author.
The incident is likely to worsen already poor relations between Russia and Ukraine, which are languishing at a post-Soviet low after Moscow's annexation of Crimea last year and its support for armed separatists in eastern Ukraine.
The Kremlin denies its forces have helped the rebels.
Investigators said Sharina, who has been in charge of Moscow's Library of Ukrainian Literature since 2011, had distributed the writings of Korchinskiy even though Russian authorities had previously banned them as extremist.
"The investigation is continuing," Russia's Investigative Committee said in a statement.