The ceasefire in Syria is to be extended by 48 hours after the United States and Russia agreed that despite sporadic violence, the truce was largely holding.

Key points: Ceasefire deal requires weeklong truce first

Ceasefire deal requires weeklong truce first Second stage involves military strikes against Nusra Front, Islamic State militants

Second stage involves military strikes against Nusra Front, Islamic State militants Focus to get immediate aid to Aleppo

The ceasefire deal was brokered by US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov last Friday and took effect on Monday night.

US State Department spokesman Mark Toner said Mr Kerry and Mr Lavrov spoke by telephone on Wednesday and agreed it was worth extending the truce.

Under the deal, the United States and Russia are aiming for reduced violence over seven consecutive days before they move to the next stage of coordinating military strikes against Nusra Front and Islamic State militants, which are not party to the truce.

"There was agreement that as a whole, despite sporadic reports of violence, the arrangement is holding, and violence is significantly lower in comparison with previous days and weeks," Mr Toner told a briefing.

The Syrian Observatory for Human Rights said no deaths from fighting had been reported in the first 48 hours of the truce.

Graves and burial mounds at the Rukban camp where there has only been one delivery of food aid in three months. ( Amnesty International )

Meanwhile, Amnesty International called on world leaders to help solve Syria's refugee crisis, releasing footage of a camp for 75,000 refugees trapped in the desert in an area known as The Berm, near the border with Jordan.

Amnesty said the images showing makeshift graves and burial mounds offered a rare glimpse inside the no man's land between the two countries where refugees were stranded, cut off from humanitarian aid.

Jordanian authorities sealed off the Rukban and Hadalat border crossings after an attack that killed seven border guards on June 21.

Since then, the only food drop was in August and resident Abu Mohamed said the humanitarian situation at the Rukban camp had deteriorated sharply.

"The situation of children in particular is very bad. We have drinking water but hardly any food or milk … [it] is awful, many people have died" he said.

"They distributed just rice and lentils and a kilo of dried dates, but that was all for a whole month, they gave us nothing but that.

"The mood among the people in Rukban is below zero."

Amnesty's video footage shows two makeshift grave sites in Rukban revealing dozens of burial mounds close to refugee tents.

Sorry, this video has expired Footage of graves in Rubkan Camp in The Berm ( The Tribal Council of Palmyra and Badia )

"The situation at The Berm offers a grim snapshot of the consequences of the world's abject failure to share responsibility for the global refugee crisis," Amnesty International's crisis response director Tirana Hassan said.

"In some cases people are suffering or even dying from preventable illnesses, simply because they are not allowed into Jordan.

"The authorities have blocked access for aid, medical treatment and a meaningful humanitarian response."

Amnesty called on Jordan to grant immediate entry to refugees at The Berm, ahead of two high-level refugee summits in New York next week.

It has also called on world leaders at the summits to commit to taking a share of refugees to relieve the pressure on Syria's neighbours including Jordan which is hosting 650,000 refugees.

Food aid still to reach Aleppo

There is continuing international pressure for all sides to allow food aid convoys to reach besieged areas, especially Syria's second main city of Aleppo, the scene of fierce fighting in recent months.

United Nations Secretary-General Ban Ki-moon called on Russia and the United States to do more to ensure aid delivery now the ceasefire was largely holding.

"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 cooperate," Mr Ban siad.

The UN said two aid convoys, each of around 20 trucks carrying mostly food and flour, that were headed for the city of Aleppo had been held up since crossing the Turkish border.

The special envoy for Syria, Staffan de Mistura, said the United Nations was waiting for Damascus to issue letters authorising the aid deliveries.

The UN estimated more than 500,000 people are living under siege in Syria after a five-year civil war which has killed hundreds of thousands of people and displaced more than 11 million.

Reuters/AFP