BEIRUT — The Syrian cease-fire, which seeks to allow the delivery of humanitarian aid and to revive peace talks, appeared to be holding on Tuesday despite sporadic and minor violations.

The deal, hammered out last week by Secretary of State John Kerry and his Russian counterpart, Sergey Lavrov, came into effect at sunset on Monday. The Syrian army said it would abide by the cease-fire until midnight Sunday, while maintaining its right to defend itself against any violations.

Syria’s largest insurgent groups have expressed misgivings about the deal, which allows for strikes against the Islamic State and Al-Qaeda-linked militants who fight alongside the rebels. Jabhat Fatah al-Sham, an Al-Qaeda-linked group previously known as the Nusra Front, has denounced the agreement.

The deal marks the second attempt this year to try to reduce violence in Syria, where the five-year civil war has killed more than 250,000 people and displaced half the country’s population of 11 million. A truce in late February collapsed weeks later.

The first week of the truce will be crucial. During that time, all fighting between Syrian President Bashar Assad’s forces and many of the rebels should stop. However, Assad’s forces can continue airstrikes against the Islamic State group and Al-Qaeda-linked militants.

If the calm holds for seven days, the US and Russian militaries would set up a new center to coordinate strikes against Islamic State and Jabhat Fatah al-Sham.

Under the truce, Assad’s forces are no longer supposed to bomb other Syrian rebels. The Syrian air force has been dropping barrel bombs on civilian areas under the pretext of targeting militants.

For the moment, ‘‘calm is prevailing in all areas,’’ said Ahmad al-Masalmeh, an opposition activist in the southern province of Daraa — where the 2011 uprising began.

In the northern city of Aleppo, which has seen heavy fighting in recent months, opposition activists said rebel-held parts were calm on Tuesday morning but many people were still hunkering down in their homes, fearful of going out. Aleppo-based activist Baraa al-Halaby said no aid deliveries have yet entered the contested area.

Syrian state news agency SANA said rebels fired three shells at a government-held neighborhood in Aleppo.

Rami Abdurrahman, head of the Syrian Observatory for Human Rights, said there were minor violations in central Hama province. Another activist group, the Local Coordination Committees, reported shelling in Aleppo and the southern region of Quneitra.

Al-Manar TV, run by the Lebanese militant group Hezbollah, said Syrian troops struck a Jabhat Fatah al-Sham tank with a missile in Quneitra, without providing further details. Hezbollah is fighting alongside Assad’s forces.

The Britain-based Observatory, which relies on a network of activists, said no one has been killed or wounded since the truce went into effect.

Turkey’s state-run news agency said 20 UN trucks have left Turkey to deliver humanitarian aid to Aleppo.

The deal’s architects hope the cease-fire will lead to an extended period of restraint that can serve as the foundation for peace talks.

In other developments, the Syrian military said Tuesday it had shot down two Israeli aircraft — a warplane and a drone — near the Israeli-controlled part of the Golan Heights.

The Israeli military quickly denied the claim.

The Israeli military said ‘‘two surface-to-air missiles were launched from Syria after the mission overnight to target Syrian artillery positions’’ but the safety of Israeli planes was not compromised.