Russian authorities say 19 students and faculty members at a college in Crimea have been killed, many of them teenagers, in a bomb-and-gun attack they say was carried out by a student who fatally shot himself after the assault.
It was not clear whether the death toll included the alleged attacker.
At least 50 others were injured in the October 17 attack at a polytechnic college in the city of Kerch, the only major outbreak of violence in Crimea since Russia seized the Black Sea peninsula from Ukraine in 2014.
News of the bloodbath unfolded quickly and chaotically, with some initial reports saying it was a gas blast and authorities later saying that it was a bomb and that they were treating it as a terrorist act.
But Russia's main investigative agency later said authorities believe an 18-year-old student at the college rampaged through the building with a rifle, shooting students and faculty members.
Investigative Committee spokeswoman Svetlana Petrenko said authorities believe the suspect, fourth-year student Vladislav Roslyakov, fatally shot himself after the attack.
She said investigators had recategorized the probe into the attack as a case of murder rather than terrorism. There was no immediate word on a possible motive.
Most or all of the victims appeared to have died of gunshot wounds, according to Petrenko, who also said that a shrapnel-packed bomb exploded at the college.
Interfax and state-run RIA Novosti news agencies quoted sources as saying a second explosive device was found and defused at the college by bomb-disposal crews.
The Russian-imposed head of Crimea, Sergei Aksyonov, said that the suspect acted alone, but some eyewitnesses spoke of at least two attackers.
In a video posted on the Internet, a woman identified as college director Olga Grebennikova said there were "many corpses, many corpses of children" and called it "a real terrorist act."
The woman, speaking on a mobile phone, suggested that multiple assailants attacked the college, throwing explosive devices and firing guns shortly after she left for a meeting elsewhere.
"They ran up to the second floor with automatic rifles -- I don't know with what -- and opened doors...and killed everyone they could find," she said, seeming to choke back tears at times.
Journalist Yekaterina Keizo told RFE/RL that when she got to the scene at about 12:30 p.m. local time, "they were carrying the injured out of the building."
"More and more ambulances were arriving every minute, but there were not enough," Keizo said. "They were putting people with IV drips into regular [minivans]."
She said that eyewitness told her that "two men" had entered the college and that "one blew himself up in the cafeteria" while the other "walked around the rooms and shot everybody indiscriminately. He just shot everyone he saw."
In other harrowing accounts, several students spoke of gunfire at the college but not a bomb blast.
The Russian newspaper Komsomolskaya Pravda quoted student Semyon Gavrilov as saying he woke up to the sound of shooting after falling asleep in a lecture and then saw a young man firing at people with a rifle.
"I locked the door, hoping he wouldn't hear me," the paper quoted Gavrilov as saying.
He said he saw dead bodies on the floor and charred walls, presumably from a fire or explosion, after police arrived about 10 minutes later to evacuate people from the building.
The Russian-imposed head of Crimea, Sergei Aksyonov, said that the suspect acted alone, but there was no immediate word of a possible motive.
When Russian authorities said they suspected it was a terrorist attack it seemed certain to increase tension between Russia and Ukraine, which Moscow has accused in the past of seeking to carry out acts of sabotage in Crimea.
The regional Emergency Situations Ministry declared a state of state of emergency in Crimea and said security was being increased.
A three-day mourning period was announced by the Russian authorities who control the Black Sea peninsula.
Meanwhile, residents of Kerch started to lay flowers at the site of the attack and a memorial service for the victims took place in the Crimean capital of Simferopol, TASS news agency reported.
Russian President Vladimir Putin voiced condolences to victims and their loved ones and ordered the authorities to evacuate badly injured victims by air to "leading" hospitals in Moscow and other cities, the Kremlin said.
At a meeting in the Russian Black Sea resort city of Sochi with Egyptian President Abdel Fattah al-Sisi, Putin declared a moment of silence for the victims and said the attack would be "carefully investigated."
Ukrainian President Petro Poroshenko took to Twitter to express his condolences to those who lost their love ones in the tragedy, emphasizing that Kyiv and the international community consider Russia's control over Crimea illegal.
“Crimea is a Ukrainian territory and Ukrainians living on the peninsula are citizens of our state," he wrote. "When Ukrainian citizens perish, wherever this happens, this is a tragedy.”
Kerch is the site of the western end of a newly built bridge linking Russia to Crimea, which it took over by force after Moscow-friendly Ukrainian President Viktor Yanukovych was pushed from power in February 2014 by pro-European protests and fled to Russia.
Russia sent troops to the peninsula, secured key buildings, and staged a referendum denounced as illegitimate by Ukraine, the United States, and a total of at least 100 countries. Only a handful of countries consider Crimea part of Russia.
Rights activists say Russian authorities have used the courts and law enforcement to conduct a campaign of reprisals against Crimeans who opposed the takeover.
Explosions in former Soviet republics are often caused by household cooking or heating gas, but Russia has also been hit by many terrorist bombings since the separatist wars in Chechnya in the 1990s and early 2000s.
The wars were followed by an Islamist insurgency in the North Caucasus region, east of Crimea, and insurgents have claimed responsibility or been blamed for most of the bombings and other attacks in Russia over the years.
School shootings were once virtually unheard of in former Soviet republics, but there have been several in Russia in recent years.
Twenty children and teenagers have been killed in attacks at Russian educational institutions in 2017-18, and 30 others have been injured.