US and Russian aircraft came within three metres (10ft) of colliding this week over the Black Sea; Barack Obama and Vladimir Putin gave each other the death stare at the G20 summit; and Obama’s Democrats have accused the Russians of hacking into their computer systems.

The relationship between Washington DC and Moscow is never easy. But it appears the two are edging towards a deal that will lead to them operating almost as a joint force in Syria.

The ambition of the deal being hammered out between John Kerry, the US secretary of state, and Russia’s foreign minister, Sergei Lavrov, in Geneva on Friday is extraordinary.

And it is not universally admired, having raised suspicions not only among moderate Syrian opposition groups but also at the Pentagon, where there is concern that Kerry may be blinded by a desire to remove the great stain on his foreign policy record before he stands down.

John Kerry and Sergei Lavrov meet in Geneva on Friday. Photograph: Kevin Lamarque/AP

The essence of the technically complex deal was set out in a letter to the opposition groups written by Michael Ratney, the US special envoy on Syria. “The main features of the agreement,” he wrote, “are that Russia will prevent [Syrian government] regime planes from flying, and this means that there will not be bombing by the regime of areas controlled by the opposition, regardless of who is present in the area.”

That, he added, would include areas in which Jabhat Fatah al-Sham has a presence alongside other opposition factions. In July the militant group changed its name from Jabhat al-Nusra in an effort to distance itself from al-Qaida, but the US still regards it as a terrorist organisation and a legitimate target. One stumbling block in talks over a deal has been how majority Jabhat Fatah al-Sham areas can be designated.

Ratney said that in return for the grounding of Bashar al-Assad’s air force, the US “would offer Russia coordination from our side to weaken al-Qaida in Syria. This coordination includes an understanding that there will not be bombings by the regime or random bombings by Russia.”

He continued: “Before we implement any agreement, we told the Russians that they and the regime must stop attacks on the opposition and recommit to the ceasefire. We have set a high ceiling for conditions.”

He said those conditions included a lifting of the siege on Aleppo, Syria’s second city and the scene of the worst carnage in Syria.

In eastern Aleppo, 250,000 citizens have endured a sustained bombing campaign and watched as rebels have tried to prevent the government from cutting off all supply routes. The Americans said the deal involved withdrawal of the regime from the chief supply route, the Castello Road, ending fighting around Ramouseh Road, allowing for the entry of humanitarian aid to Aleppo through both Ramouseh and Castello roads, and the ending of all offensive attacks and operations in all parts of the country.

America has said these pullbacks must happen before the US and Russia can implement any agreement. An official travelling with Kerry on his plane to Geneva stressed the importance of the lifting of the Aleppo siege, saying: “We need to see a situation where it’s clear within whatever is being agreed with the Russians that there won’t be a siege of Aleppo.”

One of the chief pitfalls in the negotiations will be the extraordinary effort that has been made by both the US and Russian military to draw up a map of northern Syria setting out legitimate targets for bombing.

It is relatively easy to designate Islamic State areas, or indeed civilian areas. But it has been harder to disentangle legitimate Syrian opposition groups from Jabhat Fatah al-Sham, especially in the event of pragmatic co-operation between anti-regime groups on a crowded and fluid battlefield.

John Kerry and Sergei Lavrov sit down to talks in Geneva. Photograph: Kevin Lamarque/AFP/Getty Images

European diplomats claim there is a basic problem of trust between the US and Russia that requires America to try to seek guarantees from Moscow on how it would sanction the Syrian government if its air force is not grounded. The Americans also claim the Russians are not as willing to hold back from generalised bombing strikes when the plan requires precision and targeting.

The purpose of the ceasefire also needs to be understood. It would allow the return of humanitarian convoys into besieged cities, something that the Syrian government has been blocking, leading to huge frustration among aid groups.

But it is also designed to restart substantive peace talks. The Syrian high negotiations committee produced this week its detailed democratic blueprint for a transition away from the Assad regime to a new unitary state, but the plan, praised by the British foreign secretary, Boris Johnson, was ridiculed by the Syrian government.

Previous talks about a transition in Geneva in the spring ground to a halt as the Syrian government stonewalled and played for time. There is little public sign that Russia, or the military balance in Syria, has changed the political dynamic sufficiently for a breakthrough if any fresh talks do get under way.

This week Johnson described Syria as the single most urgent political issue facing the world. But for many the future of Syria may not lie in Geneva, but instead in the talks Hillary Clinton holds on Friday with a group of highly experienced security advisers. Kerry may be eager to solve the administration’s great foreign policy conundrum, but the ugly truth is many eyes are already moving from the pronouncements of Kerry and Obama to those of the next commander-in-chief in Washington.