The remains of thousands of people believed to be victims of Stalin's Terror have been discovered in Ukraine's southern city of Odessa, local authorities said on Wednesday.
The bones of between 5,000 to 8,000 people were found in over two dozen graves close to Odessa's airport, making it one of the largest mass graves unearthed in Ukraine so far.
Sergiy Gutsalyuk, the head of the regional branch of the National Memory Institute, believes they were executed in 1930s by Stalin's notorious NKVD secret police unit, a precursor to the late Soviet-era KGB.
Gutsalyuk told AFP that the number of victims may increase as the excavations continue.
The remains were discovered after exploratory works started as part of plans to expand the airport's territory, he said.
Some mass graves had already been unearthed in the area in previous years, he added.
The prisoners' nationalities and the crimes for which they were sentenced to die remain unknown.
But the historian said that the executions date back to 1937-39, the time known as Stalin's Great Terror.
Gutsalyuk said it would be impossible to identify the victims as documents of that era are classified and kept in Moscow.
"These documents will never be handed over to us under the current government in Russia," he said.
Ties between the ex-Soviet countries have deteriorated sharply since Russia annexed Crimea in 2014 and threw its weight behind armed separatists in eastern Ukraine.
According to estimates made by Ukrainian historians, hundreds of thousands of Ukrainians were imprisoned or executed in Gulag camps during the Stalinist repressions in the 1930s.
One of the best-known execution sites is the forest near the village of Bykivnia on the outskirts of Kiev, where tens of thousands of victims were buried in 1937-1941.
Millions of Ukrainians also died in the great famine of 1932-1933, which Ukraine regards as a genocide orchestrated by Stalin.