BEIRUT — A U.S. and Russian-brokered cease-fire brought relative calm to parts of Syria for the first time in years on Saturday despite numerous cease-fire breaches, but the war against the Islamic State group continued as the extremists launched a surprise attack on a northern border town.

The Islamic State group, which is not a party to the cease-fire, launched several attacks after the truce went into effect, including a brazen offensive on the northern town of Tal Abyad on the border with Turkey and at least one suicide bombing in central Syria.

The cease-fire went into effect across Syria at midnight, marking the most ambitious international attempt yet to reduce violence in the devastating conflict, which has killed more than 250,000 people, wounded a million and created Europe’s worst refugee crisis since World War II.

Syria’s state-run news agency said armed groups fired several shells on residential areas in the capital in the first breach of a cease-fire at midday Saturday. SANA says the shells were fired by “terrorist groups” entrenched in Jobar and Douma, two opposition-held Damascus suburbs.

Rebel groups said they have registered numerous violations by government forces. Lt. Col. Fares al-Bayoush, commander of a U.S.-backed rebel faction, told The Associated Press his group and others affiliated with the mainstream Free Syrian Army are so far abiding by the truce.