WASHINGTON — The United States and Russia will try again to stop Syria’s civil war and forge a new counterterrorism partnership when their top diplomats meet next week in Geneva, U.S. officials said Thursday.

Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov will gather on Aug. 26, with the talks possibly lasting for two days. At the meeting, officials said, the sides will try to secure a cease-fire between Syria’s government and rebels and a new U.S.-Russian arrangement to share intelligence and coordinate military to defeat the Islamic State group and al-Qaida.

The diplomacy comes amid fierce fighting in Aleppo, Syria’s largest city, and new Russian bombing operations in Syria originating from an Iranian air base.

Russia and Iran have backed Syrian President Bashar Assad’s government in its five-year conflict against opposition groups that range from Islamist extremist groups such as the Nusra Front, an al-Qaida spinoff, to forces purporting to support a secular, inclusive country. The U.S. supports what it calls the “moderate” opposition.

Despite sharp differences in their interpretations of the conflict, the former Cold War foes have been weighing a partnership against their mutual enemies: IS and al-Qaida.

As part of the deal, U.S. officials said Russia would have to halt offensives by Assad’s government, something it has failed to do over months of diplomatic efforts. They said the U.S. must get rebels to break ranks with Nusra, a task that may be more difficult after its fighters successfully broke Aleppo’s siege earlier this month.

The officials weren’t authorized to speak publicly on the matter and demanded anonymity. They cautioned that the time and place of Kerry’s meeing with Lavrov may yet change.

Syria’s civil war has killed as many as a half-million people since 2011. Millions have fled as refugees, contributing to a global migration crisis. IS has seized on the instability to become a worldwide threat.

The Russian military said Thursday it was ready to back a U.N. call for weekly cease-fires in Aleppo, as haunting footage of a young boy’s rescue from a bombed-out building shook global media. The U.S. wants a long-term truce that allows not only humanitarian aid into the city, but the possibility for U.N.-brokered peace talks to resume and the start of peace process.

Thursday also marked the fifth anniversary of President Barack Obama’s call for Assad to leave power. With Russia protecting Assad’s position, the U.S. has backed off from demanding his ouster in any early phase of a political transition.

Last month, Kerry met Russian President Vladimir Putin and Lavrov in Moscow, hoping to finalize the new strategy. After two days of talks, each side spoke vaguely of steps they would take to try to stop the Arab country’s relentless bloodshed.

The discussions came shortly after a leaked proposal showed the U.S. offering Russia a broad new military partnership against IS and Nusra. Several conditions would apply, including Russia committing to grounding Syria’s bombers and starting a long-sought political transition process.

But the talk of intelligence and targeting sharing, and even joint bombing operations, quickly prompted significant dissent within the Obama administration.

Defense Secretary Ash Carter and National Intelligence Director James Clapper each voiced strong reservations about entering into such an alliance, given the administration’s repeated criticism that the Russians have primarily targeted moderate anti-Assad rebels and not IS.