BEIRUT — Russia said Wednesday that separating Syrian rebels from ‘terrorists’ is a “key task” to ensure that the Russia-U.S.-brokered cease-fire continues to hold in Syria, where a relative calm has prevailed since the truce went into effect two days ago.

The cease-fire deal was reached over the weekend after marathon negotiations between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov. Underscoring the complexity of the new arrangement, the deal was not made public in its entirety even as it came into effect at sunset Monday.

By midday Wednesday, there were no reports of major violations of the agreement, which calls on all parties to hold their fire, allowing only for airstrikes against the extremist Islamic State group and al-Qaida’s affiliate in Syria, known as Jabhat Fatah al-Sham.

One of Syria’s most powerful factions, Jabhat Fatah al-Sham’s battlefield alliance with other insurgent groups makes it difficult for the United States to target them without the danger of inflicting harm on other opposition groups.

The agreement is also to allow for humanitarian aid to reach besieged areas, with the rebel-held part of the northern city of Aleppo as a priority.

However, some 20 trucks carrying U.N aid and destined for rebel-held eastern Aleppo remained in the customs area on the border with Turkey on Wednesday “because of lack of de facto assurances of safe passage by all parties,” Jens Laerke, deputy spokesman for the U.N. office for the Coordination of Humanitarian Affairs told The Associated Press in an email.

The trucks are carrying mostly food items, and are destined for the residents of eastern Aleppo, estimated at 250,000. Details of who is to distribute the aid are also still being worked out.