An artillery exchange in eastern Ukraine between government troops and Russia-backed rebels claimed nine lives on today, casting doubt on the already shaky cease-fire.

The fighting between Russia-backed separatist rebels and Ukrainian government troops in the country's industrial heartland eased after a truce was signed in February. But despite pledges to withdraw heavy caliber weapons from the front lines, both sides seem to be engaged in recent heavy fighting.

The conflict has killed an estimated 6,400 people since April 2014, according to the United Nations.

The rebel mouthpiece Donetsk News Agency said artillery fire killed three people in a front line town of Horlivka and two in the rebel capital of Donetsk. Ukrainian officials reported two civilian deaths on their side, in a suburb of Mariupol on the Black Sea. The Ukrainian Security and Defense Council also reported two troops killed and six injured overnight.

The shelling came after failed talks between Ukraine, the rebels and the Organization for Security and Cooperation in Europe which were supposed to agree on further steps to withdraw weaponry.