Ukraine's army on Saturday reported the first death of a soldier in weeks and accused Moscow-backed rebels of sharply escalating attacks that have redoubled fears of an imminent Russian invasion.

The joint military command for east Ukraine said a soldier received a fatal shrapnel wound in the conflict zone running across two separatist regions near the Russian border.

Ukraine's emergency service said two of its staff were wounded during a wave of attacks on Friday.

The armed forces said rebels had used 82 and 120 millimetre-calibre mortar shells -- banned under previous ceasefire deals -- in towns across the front running through the eastern regions of Lugansk and Donetsk.

Separatist fighters are "firing artillery rounds on population centres and placing their artillery systems near residential homes," the Ukrainian army said.

"This way, our enemy is trying to force our armed forces to return fire and then blame them for shelling civilians," it said.

The military added that it was continuing to "rebuff and contain the armed aggression" without attacking civilians, and accused Russia of directing its allies' attacks. 

Moscow formally denies being involved in the conflict and calls it a Ukrainian internal affair.

But monitors from the OSCE European security body have reported regular shipments of Russian weapons across the border throughout the eight-year war.

The OSCE reported a massive 870 ceasefire violations across the conflict zone in its latest report Friday, which referred to incidents the previous days.

"In recent days, the OSCE Special Monitoring to Ukraine (SMM) has observed a dramatic increase in kinetic activity along the contact line in eastern Ukraine," the OSCE said in a statement.

Rebel leaders accuse the Ukrainian armed forces of trying to retake their two separatist regions by force -- a claim Kyiv denies.

The rebel leaderships in Donetsk and the smaller Lugansk region on Saturday both called the situation "critical" and announced a "general mobilisation".

Emergency over Ukraine refugees

A Russian region bordering Ukraine declared a state of emergency on Saturday citing growing numbers of people arriving from separatist-held areas in Ukraine after they received evacuation orders.

"Given the trend of increasing numbers of people arriving, we consider it appropriate to introduce a state of emergency," the Rostov region's governor Vasily Golubev said in a meeting, according to Russian news agencies.

The leaders of two pro-Russian separatist republics in eastern Ukraine on Friday ordered civilians to cross the border into Russia, accusing the Ukrainian army of preparing to try and retake the regions by force.

The conflict in eastern Ukraine erupted in 2014 when Moscow-backed rebels broke away from Kyiv and Russia annexed the Crimean peninsula. Some 14,000 people have been killed in fighting since then.

The current head of Russia's emergencies ministry said some 400 people as well as 150 vehicles were involved in operations to receive people arriving from separatist territory.

Emergency services in the Donetsk separatist region said earlier Saturday that just over 6,600 people have been evacuated.

State-run news agency RIA Novosti reported that those crossing checkpoints were being offered medical and psychological support.

The Lugansk region meanwhile said 25,000 people had left of their own accord and convoys were readying to take out an additional 10,000 people.

Russian President Vladimir Putin ordered his government late Friday to give evacuees 10,000 rubles (about 100 euros).

Kyiv has repeatedly denied any plans to regain control of separatist-held areas by force.