Russian fighters killed along with insurgents in eastern Ukraine

DONETSK, Ukraine - The Ukrainian military is battling pro-Russian militias for control in the east. On Thursday in Slavyansk, insurgents shot down a Ukrainian helicopter, killing at least 12 soldiers and a top general.

CBS News has been learning more about the militias.

Russian fighters have long been accused of taking part in the fight here. And on Thursday we got confirmation at the morgue where rebels are still counting their dead.

Officials told us they've identified 33 Russian nationals among those killed this week. They showed us coffins that they said would to be taken back home to Russia.

The coffins of Russian nationals killed fighting alongisde insurgents in eastern Ukraine will be sent to Russia. CBS News

We learned the coffins themselves were empty and they had to collect the bodies themselves from an ice cream factory where the corpses were being kept cold.

It was a gruesome scene. But they wanted to show us that Russians are part of this fight.

"We already have fighters from all over Russia," rebel leader Denis Pushilin told us.

They are counting on even more help.

Have they made a request to the Russian government for help?

"Yes, we have asked before," he said, "but now we have sent an official request in writing to Russian President Vladimir Putin."

But with or without Russia's help, the separatists say they're not standing down.

A fighter sat in front of a bulldozer outside an ex-administrative building. Is he afraid that this will come under attack?

"Nyet, nyet," he said, smiling.

"No," he told us, "we're not afraid. Do you understand? We are ready to fight."

We are seeing a lot more heavily armed men in Donetsk and heavy weapons, including the kind capable of shooting down a Ukrainian helicopter as in Thursday's attack.