Syrian government forces and their Russian allies launched a major new offensive on opposition-held areas of Aleppo on Friday, bombarding the city with dozens of airstrikes and threatening to launch a ground invasion.

The escalation was the clearest sign yet that efforts to restore a cease-fire that ended this week had failed, and that the Syrian government had returned to trying to stamp out the rebel movement and seize ground through military force.

The bombing Thursday night and Friday morning shook the ground and made streets impassible, according to antigovernment activists in Aleppo.

“There are no more roads to walk on,’’ said Zaher Azzaher, an Aleppo activist reached through WhatsApp. “Even between our neighborhoods, the roads are full of rubble and destruction.’’

The assault Friday on Aleppo left residents buried in the debris, including a child in the Marja neighborhood of the city.

The Syrian Observatory for Human Rights, which opposes the government and tracks the conflict from Britain, said at least 27 people had been killed in the overnight bombardment of Aleppo. Aid workers in the city said the death toll was higher, and deadly bombings were reported in other parts of northern Syria as well.

“You don’t know if you might stay alive or not,’’ said Modar Shekho, a nurse at al-Dakkak hospital in opposition-held eastern Aleppo.

Ammar al-Salmo, head of Aleppo’s Civil Defense Force, a volunteer rescue organization, said that three of his group’s centers had been bombed, and that some of their rescue vehicles had been knocked out.

“It is as if Russia and the regime used the truce only to maintain their weapons and plan on next targets,’’ Salmo said from Aleppo. “It is like doomsday today in Aleppo.’’

The Syrian government announced the new offensive in its state-controlled news media Friday, quoting an unnamed Syrian military official who described the Aleppo operation as “comprehensive’’ and said it could continue for some time. The official said the operation would “include a ground offensive.’’

That appeared unlikely, as many analysts have said that the Syrian miliary does not have the manpower to seize and hold significant territory. Its air force, however, is able to pummel rebel-held areas.

The intensified assault on Aleppo came after efforts to revive a partial cease-fire in the conflict stalled in New York, where diplomats from the International Syria Support Group had been meeting on the sidelines of the UN General Assembly annual session.

Secretary of State John Kerry met informally Friday with his Russian counterpart, Sergey V. Lavrov, and told reporters that their talk had yielded “a little bit of progress.’’

Kerry gave no further detail, and it remains unclear whether Russia is willing to accept his proposal for a flight ban over critical areas in Syria.

Speaking at his own news conference, Lavrov said the United States had failed to ensure that moderate Syrian rebels separated themselves from extremist militants of the Qaeda-allied Nusra Front. Until that happens, Lavrov said, any other measures would be “senseless.’’

Jean-Marc Aryault, the foreign minister of France, one of the members of the International Syria Support Group, said earlier Friday that he feared the diplomatic paralysis reflected a growing weariness with the daily horrors of the Syrian war.

“Will we be inured to this?’’ he asked. “Let’s not let Aleppo become the 21st-century Guernica.’’