Cross-border humanitarian aid to Syria remains vital for the lives of millions, UN Secretary General Antonio Guterres said in an internal report on Tuesday.
It comes as a UN authorisation allowing aid into rebel-held areas in the country's north-west without approval from Damascus is up for renewal.
A rare moment of co-operation between the US and Russia in July allowed a six-month extension of activity at Bab Al Hawa, the only border crossing through which aid reaches the rebel stronghold of Idlib province.
The authorisation, renewable once, runs until January 10.
"Cross-border assistance remains lifesaving for millions of people in need in north-west Syria," Mr Guterres said in a confidential document obtained by AFP.
He said more than four million people were in need of crucial assistance across the country.
The US and several European nations believe the UN authorisation for the crossing between Syria and Turkey should renew automatically for an additional six months, without the need for a new vote.
But Russia, a key ally to the Damascus regime, has previously opposed the move, invoking Syrian sovereignty.
Moscow has linked any potential extension to Tuesday's report, as well as a possible new vote.
The cross-border mechanism has been operating since 2020 through Bab Al Hawa, after the Russian-imposed removal in 2019 of three other access points in Syria.
In Tuesday's document, the UN chief refers to another project for humanitarian operations, this time across the front lines, to reach Idlib.
"If implemented, this plan will make operations across the front lines more predictable and effective," Guterres said.
However, he insisted upon the importance of the Bab Al Hawa crossing.
"At this point such cross-line convoys, even if deployed regularly, could not replicate the size and scope of the cross-border operation," he said.
Mr Guterres said some 4.5 million people in Syria need help this winter, up 12 per cent from the previous year, because of the economic crisis and the Covid-19 pandemic.
Only 2.9 per cent of the Syrian population is fully vaccinated, according to the report.
More than three million people live in Idlib province, much of which is controlled by jihadists and allied rebels.
In June, the UN said around 2.4 million people there were in need of humanitarian aid.
In pictures - Syria's Banksy struggles to survive in Idlib
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Abu Malek Al Shami colouring the 'Suffering Heart' mural. Abd Almajed Alkahr/The National -
Like Banksy, he has become known for his striking, colourful murals. Abd Almajed Alkahr/The National -
Al Shami draws a mural called 'Syria Game'. Abd Almajed Alkahr/The National -
Al Shami and his friends work on a mural in Kafranbel in 2017, which points to the 1,800 victims in Syria of chemical weapons. Photo supplied by Abu Malek Al-Shami -
Al Shami and his friend finish the mural. Photo supplied by Abu Malek Al-Shami -
An image of Al Shami and Majd Mohadamani in 2014 in Daraya, in front of a mural in a ruined school. Photo supplied by Abu Malek Al-Shami -
Al Shami looks at his finished picture. Abd Almajed Alkahr/The National -
Al Shami drawing in his studio. Abd Almajed Alkahr/The National -
Abu Malek Al-Shami in his studio in Idlib. Abd Almajed Alkahr/The National -
Al Shami holding a roller brush looking at the mural 'Syria Game'. The mural appears on a ruined roof. Abd Almajed Alkahr/The National -
Al Shami puts the finishing touches to his picture based on Vincent Van Gogh’s 'The Starry Night'. Abd Almajed Alkahr/The National -
The winter of 2019 in Dair Al-Zugub, in North Idlib, Al Shami draws on a ruined roof as the sun is about to set. Abd Almajed Alkahr/ The National -
Al Shami has been hailed as 'Syria's Banksy', after the internationally-renowned graffiti artist. Abd Almajed Alkahr/ The National -
Al Shami looks at the mural he has drawn on a devastated roof in Dair Al-Zugub in Idlib. Abd Almajed Alkahr/ The National
