SCHASTYE, Ukraine (AP) — Separatist rebels and Ukrainian forces have begun pulling back smaller-caliber weapons from the front line, a step toward de-escalating a war that has killed more than 8,000 people.

Under an agreement reached week, tanks, artillery pieces and mortars with a caliber of less than 120 millimeters are to be pulled back at least 15 kilometers (nine miles) from the front line.

The agreement, to take place in phases over 39 days, follows earlier moves to pull back heavier weapons to create a buffer zone.

On Saturday, an Associated Press journalist saw three columns of rebel tanks leaving frontline areas near Schastye, in the Luhansk region. Ukrainian military spokesman Vladislav Seleznev said Ukrainian forces also were pulling back weapons. Pullback in the Donetsk region is to begin in two weeks.