Six people have been killed by Russian shelling of the town of Toretsk in eastern Ukraine's Donetsk region, Ukrainian emergency services say.

According to foreign media, Telegrafi reports, rescue teams found five bodies in the ruins of a house, while another person died in the hospital, they add.

Fierce fighting continues in the east, although Russia is slowly advancing.

Russian Defense Minister Sergei Shoigu has ordered generals to focus on destroying Ukraine's long-range missiles and artillery weapons.

The Defense Ministry said the weapons were being used to bomb residential areas of eastern Ukraine under the control of Russian-backed separatists, and set fire to wheat fields and grain storage silo towers.

The ministry also said that a Russian missile attack on Sunday in the Donetsk village of Kostiantynivka had killed up to 250 mercenaries fighting on the Ukrainian side, as well as destroyed 19 military vehicles.

The claims could not be independently verified.

In recent weeks, the US has supplied Ukraine with long-range missiles, including precision-guided High Mobility Artillery Missile Systems (HIMARS), which Kiev says are beginning to make a difference in the field of the battle.