Beirut — The Syrian government embarked on a wave of intense airstrikes against opposition-controlled areas on Saturday, killing scores of people only hours after the announcement of a new cease-fire deal between Russia and the United States.

The attacks, which killed more than 80 people in the rebel-held cities of Idlib and Aleppo, compounded skepticism expressed by the opposition that this deal will work where others have failed to end the war.

The agreement was announced early Saturday in Geneva by Secretary of State John F. Kerry and Russian Foreign Minister Sergei Lavrov after months of haggling over details. It was hailed by the two leaders as a breakthrough in the quest to bring about a negotiated settlement to the five-year-old war.

The deal goes further than a more limited one that collapsed earlier this year because it places U.S.-Russian military cooperation in the fight against terrorism at the center of the effort to end Syria’s war.

If implemented in accordance with the vision outlined by Kerry at an overnight news conference with Lavrov in Geneva, the agreement will transform the battlefield and bring about much-needed relief from the relentless suffering.

Civilians will be protected from airstrikes, desperate communities will receive all the food and medicine they need, Russia and the United States will work together to vanquish terrorists and new negotiations will begin to secure an eventual end to the rule of Syrian President Bashar Assad and his regime.

The deal does not, however, address the inherent contradictions that have scuttled past efforts to end the fighting — including the question of why Assad’s government would cooperate with a process that the United States insists is intended to lead to his departure, or whether Russia supports that goal.

It also does not explain why the group identified as the chief target of the proposed U.S. and Russian military cooperation would comply with a cease-fire intended to bring about its destruction. Kerry and Lavrov named as the main target of the proposed joint strikes the former al-Qaida affiliate Jabhat al-Nusra — which has now rebranded itself as the Front for the Conquest of Syria, or Jabhat Fatah al-Sham.

The Syrian opposition said it would have to closely study the details of the deal before reaching a decision on whether to abide by it.