KIEV, Ukraine

Pro-Russian separatists have violated the Minsk cease-fire 25 times on Thursday, Ukraine's Counterterrorism Center said in a statement.

The center said that despite the obligation to withdraw heavy weapons as stipulated in the Feb. 12 Minsk Agreement, pro-Russian separatists have attacked soldiers with 152 mm, 122 mm and 120 mm heavy-caliber weapons.

According to the statement, in last 24 hours, six Ukrainian soldiers had been injured in clashes.

The statement added the attacks had targeted Ukrainian soldiers near the villages of Peski, Avdeevka, Opitnoe, Volonvoha, Sokolniki and Mariinki villages.

The Counterterrorism Center also said that the pro-Russian separatists had attacked Ukrainian military posts near Donetsk Airport and in Shirokino borough, near Mariupol, but the military had repelled the attacks.

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

Ukrainian and European leaders have accused Russia of fueling the conflict by providing arms and ammunition to the separatists, a claim Russia denies. Moscow accuses the U.S. and the EU of deliberately destabilizing 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 April 2014, according to the U.N..