A Tu-154 crashed in eastern Ukraine en route from a Russian Black Sea resort to St. Petersburg. Pulkovo Airlines, which owned the plane, said Wednesday morning that 170 people - including 45 children under the age of 12 - had been killed. Other sources had suggested 171 passengers and crew had lost their lives.
"Ukraine shares the pain of the great loss that has befallen the friendly Russian nation," President Viktor Yushchenko's message said.
"Ukrainian President Viktor Yushchenko offered his condolences to Russian President Vladimir Putin, the families of the victims and the entire Russian people over the crash of a Russian Tu-154 airliner in the Donetsk Region on the way from Anapa to St. Petersburg," the said the Ukrainian president's press service.
The plane came down in stormy weather 45 kilometers (30 miles) north of regional center Donestk near the Russian border.
Yushchenko said Ukraine's authorities would do everything possible to establish what caused the tragedy.
Wednesday and Thursday are days of mourning in Ukraine and Russia respectively.