Syria ceasefire: UN's Ban Ki-moon makes aid plea
UN Secretary General Ban Ki-moon has urged Russia and the US to push all warring sides in Syria to allow safe passage for desperately needed aid.
Lorries with a month's food supply for 40,000 people are stuck at the Turkish border, 48 hours into a ceasefire.
Getting aid to civilians in besieged areas like the rebel-held eastern half of the city of Aleppo is a priority.
But disagreements between warring sides and concerns about safety are delaying emergency deliveries, the UN says.
Criticism has also been levelled at President Bashar al-Assad's government for trying to control aid flows.
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"It's crucially important [that] the necessary security arrangements" are made so the convoy can travel, Mr Ban said.
"I have been urging the Russian government to make sure that they exercise influence on the Syrian government, and also the American side to make sure that Syrian armed groups, they also fully co-operate."
The Syrian government says it will only allow aid co-ordinated through itself and the UN to reach Aleppo.
Meanwhile, UK-based monitoring group the Syrian Observatory for Human Rights said it had recorded no casualties in the first 48 hours of the ceasefire, contradicting earlier Russian accounts of two government troop deaths on the Castello Road, which leads to Aleppo.
US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov have agreed in a phone call to extend the truce for another 48 hours, the US State Department says.
"There was agreement that as a whole, despite sporadic reports of violence, the arrangement is holding," spokesman Mark Toner said.
Some 250,000 people are trapped in eastern Aleppo. Protests have been held against the UN as the area waits for aid but people are enjoying the temporary calm, residents say.
"The streets were always empty before," a member of the rebel Free Syrian Army, Abo Haitham, told Reuters news agency.
"But now people are coming and going, children are playing in the playground. But the downside is that the markets are empty."
In government-controlled western Aleppo, pictures showed young people relaxing outside. Before the ceasefire, districts there were regularly targeted by rebel rocket and mortar fire.
Residents of eastern Aleppo are reported to be in desperate need of fuel, flour, wheat, baby formula and medicines.
Two convoys of lorries carrying aid crossed into Syria about 40km (25 miles) west of Aleppo on Tuesday but were not allowed to go much further, Reuters reports.
One issue holding back aid deliveries is that al-Qaeda affiliates operate in the area, which may mean the main route into Aleppo is not yet safe, the BBC's James Longman in Beirut says.
The Syrian truce
- A deal was brokered by Russia and the US that began with a nationwide ceasefire from Monday between the armed opposition and the Syrian government, but not jihadist groups
- The ceasefire will be renewed every 48 hours if it holds
- It is meant to allow for "unimpeded and sustained humanitarian access" to besieged areas, including Aleppo
- If the truce holds for a week, Russia and the US will bomb militant groups together, including so-called Islamic State and Jabhat Fateh al-Sham (formerly the Nusra Front)
- The "legitimate opposition" are meant to distance themselves from such groups
- The deal has faced widespread scepticism, not least because the US backs anti-government rebel groups while Moscow is a key ally of the Syrian government
- The deal could pave the way for a political transition, the US says
Since the truce came into effect on Monday, accusations have been made against both rebels and government forces for sporadically violating it.
But it appears to have largely held.
The deal, described by Mr Kerry as the "last chance to save a united Syria", was struck on Friday in Geneva after months of talks between Russia and the US. It requires both sides to allow unhindered access for humanitarian aid.
The number of deaths recorded since the beginning of the conflict in March 2011 recently rose above 300,000, according to the Syrian Observatory for Human Rights, a UK-based monitoring group.
However, it said it estimated the full death toll to be about 430,000.
Mr Kerry said 450,000 had been "slaughtered" in an interview with National Public Radio on Tuesday.
More than 4.8 million people have fled abroad, and an estimated 6.5 million others have been displaced within the country, the UN says.
Areas of control around Aleppo
If the truce holds...
Jihadist groups like so-called Islamic State and Jabhat Fateh al-Sham face the joint might of the Russian and US air forces
Moderate rebels and civilians in the areas they hold will no longer face the threat of indiscriminate air strikes such as barrel-bombing although the Syrian air force will not be grounded completely; aid deliveries will be allowed to areas currently under siege
President Assad will be in a stronger position as the US and Russia engage two of his most effective military opponents while moderate rebels observe the truce with his forces
Syria's history of failed deals
February 2012: Syrian government "categorically rejects" an Arab League plan calling for a joint Arab-UN peacekeeping mission
June 2012/January 2014/January 2016: Three failed UN-sponsored peace conferences in Geneva
September 2013: Kerry and Lavrov negotiate a deal to strip the Syrian government of its chemical weapons in return for the US backing away from air strikes. Since then, the government has again and repeatedly been accused of using toxic chemicals against rebel-held areas
February 2016: World powers agree in Munich on a nationwide "cessation of hostilities" in Syria excluding jihadist groups. There is no agreement on any joint US-Russian operations. The "pause" quickly unravels as Assad promises to regain control of the whole country
March 2016: President Vladimir Putin declares "mission accomplished" in Syria and orders removal of "main part" of Russia's air army in Syria. Russian air strikes have continued ever since