KIEV, Ukraine

 At least six Ukrainian soldiers were killed during the pro-Russian separatists' attacks on Ukrainian troops in eastern Ukraine, according to the statement from Ukrainian Counter-Terrorism Center.

The statement Sunday claimed that pro-Russian separatists have violated the cease-fire at least ten times from Saturday night and used heavy weapons, which were withdrawn from front line according to the Minsk agreement.

Ukrainian troops did not respond to separatist attacks, the statement added.

A cease-fire was signed between Ukrainian forces and pro-Russian separatists in Minsk on Feb. 12.

The cease-fire agreement includes the withdrawal of heavy weaponry from combat areas, the withdrawal of all foreign-armed formations and release of all hostages and unlawfully detained persons, as well as political reforms and decentralization in the eastern Ukrainian regions.

Four Ukrainian soldiers died after their vehicles fired by pro-Russian separatists in Shchastya, a city in Luhansk province, the statement said.

Another two were killed after their vehicle was hit by mine in near Scirocco city, a Ukrainian port city of Mariupol.

Ukrainian and European leaders have accused Russia of supporting the conflict by providing arms and ammunition to the separatists, while Russia says the U.S. and EU have deliberately destabilized Ukraine to expand the West's military presence in Eastern Europe through NATO.

More than 6,000 people have lost their lives in the conflict between Ukrainian forces and pro-Russian separatists since last April, according to the U.N.

Meanwhile, Right Sector party leader Dmytro Yarosh has been appointed as advisor to the Chief of the General Staff.

The leader of the Ukrainian Volunteer Corps and Chief of the General Staff Viktor Muzhenko agreed to appoint Yarosh as advisor.

The Right Sector is a radical organization which helped organize EuroMaidan protests in 2014.