Three women and a man died when a shell landed in the courtyard of a private house in Avdiyvika, eastern Ukraine, late on Saturday. Another man was hospitalised with serious injuries.
The Ukrainian authorities blamed pro-Russian forces the other side of the February 2015 ceasefire line, the terms of which have been violated almost daily ever since.
Each side accuses the other of breaking the truce, but Kyiv has repeatedly warned heavy weapons supposed to have been withdrawn out of range are still being used. The army says that was the case in this incident.
The rebels say two civilians were injured in areas they control on Saturday, and did not comment on the Ukrainian claims.
There are casualties on both sides every day in this war of attrition being fought at the gates of the EU. Only last month in a serious incident a paramedic working for the OSCE monitors was killed when their vehicle hit a landmine in rebel-controlled territory.
Avdiyvika itself was the scene in January this year of one of the biggest battles in the over three-year conflict, which only calmed after over a week of intense artillery and rocket exchanges. Suspicions remain high that the rebel leaders of the self-styled Luhansk and Donetsk Republics take their orders directly from Moscow, and that Russia was behind the 2014 uprising, and any upsurge in fighting.
Russia has always denied this, and continues to deny it offers anything other than humanitarian and moral support to the two territories.
The death of the four civilians in Avdiyvika led to President Poroschenko and his wife staying away from the final of the Eurovision Song Contest, being held on Saturday night in Kyiv.