The latest round of negotiations to salvage the 2015 deal on Iran's nuclear deal started in late November and are widely expected to reach a crunch point in the coming days.

Officially, all states at the talks -- Britain, China, France, Germany, Iran and Russia, with the US taking part indirectly -- have tried to separate the talks from broader geopolitical tensions.

Russia's annexation of Crimea in 2014 did not prevent the original accord from being reached a year later.

The deal, known as the JCPOA, secured sanctions relief for Iran in return for strict curbs on its nuclear programme to prevent it acquiring an atomic weapon, something Iran has always denied wanting to do.

The other parties to the latest talks have presented a relatively united front towards Tehran. The question is whether that can survive the huge geopolitical shocks emanating from the Ukraine conflict.

"Of course the international community sees Iran as an ally of Russia in this crisis," said Iranian international relations expert Fayaz Zahed.

The war "is undermining understanding" between the countries involved and that the "situation is very fragile", he added.

- 'Intense pressure' -

Another effect on the talks could come through oil prices, which have soared to their highest level in seven years in response to the conflict and the barrage of Western sanctions against Moscow.

"Soaring oil prices will put intense pressure on Western governments, particularly the US, to deliver an agreement quickly," said analyst Henry Rome from the Eurasia Group.

The JCPOA began to disintegrate in 2018 when the then US president Donald Trump withdrew from the deal and re-imposed sanctions on Tehran.

If those sanctions are once again lifted, Iran's considerable oil reserves will return to the global market, easing the fuel price rises which are preoccupying the White House.

On the other hand, Rome says the current situation will "lessen Tehran's sense of urgency", as it is benefitting from higher prices from oil sales to China.

Iran then is in no hurry in this crucial phase of the talks, insisting on certain "red lines" concerning how many sanctions would be lifted -- and on guarantees against a repeat of Trump's actions.

"US has already 'walked away' from JCPOA," Iranian foreign ministry spokesman Saeed Khatibzadeh tweeted on Monday. "We must make sure it won't happen again."

- 'Playing with fire' -

Another key point of contention is Iran's demand that the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), close its investigation into past nuclear activity at several undeclared sites.

The IAEA's Director General Rafael Grossi has said several times that Iran's explanations on the sites have not been satisfactory.

Iran is "playing with fire", the head of the French delegation Philippe Errera tweeted on Sunday. "You have to know when you're going too far," he warned.

The Western states have repeatedly stressed the urgency of wrapping up the talks since they restarted in November. On Monday, France's foreign ministry once again said it was "critical" to close a deal this week.

US State Department Spokesman Ned Price has warned that Washington is "prepared to walk away if Iran displays intransigence to making progress".

In that case the US has made reference to a "Plan B" it would put into effect to prevent Iran gaining nuclear weapons capability.

While the history of negotiations on Iran's nuclear programme is littered with missed deadlines, Barbara Slavin of the Atlantic Council believes a deal is still within reach -- and sooner rather than later.

Given Western moves to isolate Russia from the world economy, she says, Iran "needs to reduce its dependence on what has now become a pariah state and restore at least some economic ties to Europe".