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.

Russian Lt. Gen. Victor Poznikhir said rebels had violated the truce 60 times since it came into force sunset Monday. For their part, opposition forces said they had recorded some 28 various violations by government troops on Tuesday.

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.

By evening 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.

Secretary of State John Kerry spoke to Russian Foreign Minister Sergey Lavrov on Wednesday and they agreed that "as a whole, despite sporadic reports of violence, the arrangement is holding and violence is significantly lower," State Department spokesman Mark Toner told reporters. The two diplomats also agreed to extend the current truce by another 48 hours, Toner said.

Earlier, Russia's Poznikhir had underlined Moscow's intention to extend the cease-fire by 48 hours. The Syrian government has already agreed to maintain the cease-fire until Sunday.

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 estimated 250,000 residents of eastern Aleppo. Details of who is to distribute the aid were still being worked out.

U.N. Secretary General Ban Ki-moon said humanitarian aid to Syrians was being held up by a lack of security arrangements. He said he had been in touch with the Russian government, urging them to exercise influence on the Syrian government to let the trucks in, and with the Americans to get Syrian armed groups to co-operate.

Separately, Turkey sent a pair of trucks to the Syrian border town of Jarablus to deliver food and children's toys on the third day of the Muslim Eid al-Adha holiday. Turkish ground forces joined Syrian rebels to expel Islamic State militants from the town last month.

In besieged rebel-held Aleppo, Mohammed Khandakani, a 28-year old attorney, said calm was prevailing in an area that had seen some of the heaviest violence in the days leading up to the cease-fire. "The truce is holding. There is relative relief. It is an unexplainable feeling of safety," he said. "But the anticipation and concern for the future leaves a lump in my throat. We are still living in a prison."

Khandakani is a volunteer at a medical centre in eastern Aleppo. Medical facilities in rebel-held areas have been frequent targets for government bombings.

In the lead-up to the cease-fire, 40 days of fighting in Aleppo killed nearly 700 civilians, including 160 children, according to the Britain-based Syrian Observatory for Human Rights.

Syrian state media broadcast footage of the tourism and health ministers touring neighbourhoods on the southern edge of Aleppo that were recently recaptured by the government from rebel groups. "Here is the line that separates civilization and backwardness, barbarity, the line between darkness and light," said tourism minister Bishr Riyad Yazigi, speaking in the Ramouseh area of the divided city.

Meanwhile, Syrian state media reported violations of the cease-fire in central Homs, saying that rebels fired mortar rounds Wednesday in a rural part of the province. A day earlier, the government said rebels had targeted the Castello road, the only remaining artery by which aid reaches the eastern, rebel section of Aleppo.

The chief of the Syrian Observatory for Human Rights, a monitoring group, said Wednesday there were no reported civilian casualties in the first 36 hours of the cease-fire.

"The violations are negligible. Most importantly, there were no Syrian civilian deaths," Rami Abdurrahman told the AP.

A spokesman for Russian President Vladimir Putin said the Kremlin is hopeful the truce deal "will create the necessary environment for political settlement."

"The cease-fire is quite fragile and the key task now is to wait until moderate opposition stands aside from terrorist groups. It's a key task without which further progress can hardly be possible," Dmitry Peskov told reporters in Moscow.

Russia launched its military operation in Syria last year to support ally President Bashar Assad's forces.

Vasilyeva reported from Moscow.