A long-awaited swap of prisoners between Russia and Ukraine was underway on Saturday, sources and state media said, with 70 people involved in the landmark exchange.
A Ukrainian government source told AFP the swap was proceeding and that 35 people on each side would be exchanged.
A number of high-profile prisoners are expected to be part of the exchange.
Earlier Saturday an AFP journalist in Moscow saw two buses with tinted windows leaving the high-security Lefortovo jail escorted by a police convoy.
Russia's state-run news channel Rossiya 24 said the convoy had departed "within the framework of preparations for a prisoner exchange".
The channel said the buses had arrived at Moscow's Vnukovo terminal for government flights, and that a Russian government plane had landed at Kiev's Boryspil airport.
Anticipation has been building in recent days for the swap, which would be the first major exchange of prisoners between Russia and Ukraine since the conflict over eastern Ukraine erupted in 2014.
It could be a crucial step in easing tensions between the ex-Soviet neighbours over Russia's annexation of Crimea and the war with Moscow-backed separatists that has left more than 13,000 dead.
The head of the defence team for 24 Ukrainian sailors captured by Russia last year told AFP they would be part of the swap.
"According to my information, they were put on a bus. All 24 of them," Nikolai Polozov said, adding that he expected them to arrive in Ukraine "in the next few hours".
- Sailors, filmmaker, journalist -
Moscow has been holding the sailors since seizing three vessels last November in the most dangerous direct clash between Russia and Ukraine in years.
Among other prisoners who could be released by Russia is film director and activist Oleg Sentsov, 43, who has become Ukraine's most famous political prisoner.
He was arrested in 2014 and has been serving a 20-year sentence in a Arctic penal colony for planning "terrorist attacks" in Crimea.
Reports emerged last week that Sentsov had been moved to Moscow.
Ukraine could hand over Kyrylo Vyshynsky, a journalist at Russia's RIA Novosti state news agency who was released on bail late last month pending a trial for "high treason".
A Ukrainian court this week also released from detention a man investigators have described as a key witness in the downing of flight MH17.
The release of Vladimir Tsemakh, an alleged air defence specialist for pro-Russian separatists, prompted concern from the Netherlands that he may avoid questioning.
On Thursday, Russian President Vladimir Putin said the "large-scale" prisoner exchange with Ukraine was being finalised and that the swap would be "a huge step towards normalising relations" with Kiev.
Ukrainian President Volodymyr Zelensky raised the prospect of a prisoner swap after sweeping to power in an election in April.
The comedian-turned-politician, whose defeat of incumbent Petro Poroshenko shocked Ukraine's political elite, had vowed during the campaign to bring Ukrainian prisoners home.
His election has revived peace efforts and Paris has called for a summit of the leaders of Russia, Ukraine, Germany and France to be held later this month.