The Russian-backed (with 9,000 of their own) rebels in Ukraine and Ukraine signed a cease fire agreement in September, including an agreement to withdraw their respective artillery units from that cease fire line.

Having done that,

a rebel rocket attack early Saturday morning (24 Jan) killed 29 people [at least 30 according to Reuters] in the port city of Mariupol[]

which Russia has been trying to seize for some months pursuant to their effort to open a land route to Russian-occupied Crimea. The day before,

[T]he rebels rejected a [renewed] peace deal and said they were going on a multi-prong offensive against the government in Kiev to vastly increase their territory.

Alexander Zakharchenko, leader of the Russian-backed Donetsk People’s Republic said this of the Russian/separatist forces’ plans:

Today an offensive was launched on Mariupol. This will be the best possible monument to all our dead because we will avenge them all[.]

So much for the value of a Russian commitment.