Students have been left with horrific injuries after a nail bomb went off at a college in Crimea and a gunman opened fire with a rifle.

The death toll rose to 20 on Thursday when a teenage girl died of her wounds aboard an emergency helicopter.

Russia named the killer as Vladislav Roslyakov, 18, who shot himself after the rampage at Kerch technical college.

Fifteen students and five teachers died. Ten victims are in intensive care. Russia annexed Crimea in 2014.

Some victims have had limbs amputated and the bomb blast injured 74 in total, Russian media report.

Crimea’s Russian-backed leader, Sergei Aksyonov, said on Thursday that the gunman had acted alone but must have had help in advance.

“The way me and my colleagues see it, the preparations could not have been done by this villain on his own,” he said.

‘People have lost limbs’

A huge nail-bomb blast ripped through the college’s cafeteria, before the killer stormed through the building, shooting people at close range with a pump-action hunting rifle.

Russian Health Minister Veronika Skvortsova said the explosion from a home-made device had showered people with shrapnel. “Some victims’ internal organs were ruptured, we’re finding washers and ballbearings in their livers, intestines, blood vessels.”

“Limbs have been amputated – people have lost feet and shins,” she said.

Some of the critically injured were being transferred to hospitals as far away as Moscow.

The authorities in Crimea have declared three days of mourning. A prayer service was held for the victims at a makeshift shrine near the college.

The rampage is the deadliest attack to have taken place in Crimea since Russia annexed the peninsula from Ukraine in 2014. That annexation was condemned by many Western powers.

It marked the start of a conflict pitting Russian-backed rebels in eastern Ukraine against Ukrainian government forces.

What happened at the college?

The perpetrator is said to have run from room to room as he fired. Minutes earlier he had left a rucksack containing the nail-bomb in the cafeteria on the ground floor and detonated it remotely, Russian Channel One TV reported.

Photos later emerged in Russian media purportedly showing his body in the college library.

The TV report described a scene of devastation and mass panic after the blast. It said doors and windows were shattered in the entrance hall and on the first floor, above the cafeteria. Some students leapt out of the building from a height of 5m (16ft 5in).

Investigators later said they found a second explosive device among the gunman’s possessions and that it had been disarmed. He was also reported to have several packs of bullets and home-made petrol bombs.

BBC Russian spoke to witnesses, including Igor Zakharevsky. “I was at the epicentre of the first explosion, at the entrance, near the buffet,” he said.

“I was in complete shock and one of my classmates started pulling me away. Then I heard several shots at intervals of two or three seconds. After a while there was another explosion.”

Marina, an 18-year-old student at the college, said there was “a massive explosion, the windows began to rattle and everyone started screaming”.

“We bolted out of the classroom and ran. There was complete pandemonium in the corridor,” she said. “I saw a girl lying near the wall in an unnatural position, others lying on the floor covered in blood. Shots were being fired every five or six seconds.”

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The incident was first described as a “terrorist act”, but Russia’s investigative committee later reclassified it as “mass murder”.

President Vladimir Putin said the attack was a “tragic event” and expressed condolences to the victims’ relatives.

Spate of attacks

By Steve Rosenberg, BBC News, Moscow

Until now, if you had told people in Crimea there had been a mass school shooting, most would have thought you were talking about the United States. Now all that has changed.

The shooting spree in the Kerch Polytechnic has left the peninsula, annexed by Russia from Ukraine in 2014, in shock. But should it come as such a surprise?

There have been five attacks in schools in Russia this year where a number of children were injured.

In Kerch, questions are already being asked: how did Vladislav Roslyakov manage to obtain a licence for a hunting weapon? And how was he able to launch such a deadly attack on his college?

What do we know about the alleged gunman?

His precise motives remain unclear. But there are suggestions the fourth-year student had developed a hostile attitude to the college.

Russia’s RBC TV interviewed a friend who said Roslyakov “hated the technical school very much” and had vowed “revenge” on his teachers.

It has emerged that he obtained a gun licence when he was 17. His parents are divorced.

Classmates said Roslyakov was very reserved and had long ago stopped using social networks.

College teacher Olga Mikhailichenko said he was “a hard-working student, very quiet”. A neighbour was quoted as saying “he had no friends”.

The college prepares students for engineering jobs and is reportedly well-equipped. But some students spoke of lax security there.

What is the political situation in Crimea?

The peninsula remains a flashpoint between Russia and Ukraine.

Kerch is situated at the point where Russia built a new bridge joining Crimea to Russia.

In a reminder of how poor relations are between Russia and Ukraine, the speaker of the Crimean parliament, Vladimir Konstantinov, suggested Kiev might have been behind the attack.

“The entire evil inflicted on the land of Crimea is coming from the official Ukrainian authorities”, he said.