The Ukrainian military stated that a soldier has been killed in shelling by pro-Russian separatists on Saturday morning in eastern Ukraine. This week's attack in the long-running conflict has fueled fears that the Russian military is behind it.

Following the report, Reuters cited witnesses who heard several explosions in the north of the separatist-held city of Donetsk in eastern Ukraine. The origin of the explosions was not clear. There was no immediate comment from separatist authorities or from Kyiv.

The Ukrainian military said on its Facebook page that it had recorded 19 cease-fire violations by the separatists since Saturday compared to 66 cases in the last 24 hours.

Separatists opened fire on more than 20 settlements, using heavy artillery, which has been prohibited under Minsk agreements, the military said.

Incidents of shelling across the line dividing government forces and separatists increased sharply this week, in what the Ukrainian government called a provocation. It strongly denied suggestions by Russia that Kyiv could launch an offensive in eastern Ukraine.

The Minsk accords aim to end an eight-year conflict between the Ukrainian army and separatists in the country's east.

Meanwhile, the east Ukraine breakaway region leader, the so-called Donetsk People's Republic, on Saturday said he spearheaded general mobilization, with fears mounting of war in the ex-Soviet country.

"I urge my fellow citizens who are in the reserves to come to military conscription offices. Today, I signed a decree on general mobilization," Denis Pushilin said in a video statement after war analysts warned of large-scale fighting in east Ukraine.