As officials work to get access for aid convoys, the two main players in the ceasefire deal accused each other of not meeting expectations.
Russia's Defense Ministry said Thursday that the United States was not fulfilling its obligations under the ceasefire agreement.
Washington pointed the finger right back at Moscow, accusing it of not holding up its end of the deal.
Russia said US-led "moderate opposition forces" had increased attacks on residential neighborhoods, claiming at the end of the deal's third day that "only the Syrian army observes silence mode."