A proposed round of Syrian peace talks slated for later this month appears to be on the verge of collapse, with both major parties saying they will not participate without major concessions from the other side.

The Syrian regime says it will pull out of attending because it will not endorse a meeting aimed at deposing president Bashar al-Assad.

"We will not go to Geneva to hand over power as desired by (Saudi Arabia foreign minister Prince Saud) al-Faisal and certain opponents abroad," Syria's information minister Omran al-Zohbi said.

"President Bashar al-Assad will remain head of state."

Washington, Moscow and the United Nations are trying to fix a date for the so-called Geneva II talks, to bring all sides together to discuss a political solution to the conflict.

Syria's opposition has refused to attend unless Assad's resignation is on the table, while rebel groups have warned that participants would be considered traitors.

The Syrian information minister's comments came after US secretary of state John Kerry met his Saudi counterpart Prince Saud in Riyadh to smooth over differences on Syria.

The top US diplomat was hastily dispatched to Riyadh to patch things up after rare complaints over Washington's policies on both Syria and Iran.

Saudi Arabia expressed anger after US president Barack Obama stepped back after threatening a punitive strike against Syria over August's chemical weapons attack near Damascus.

While Mr Kerry reiterated that Washington opposes military intervention to end the bloodshed in Syria, Prince Saud said negotiations "shouldn't just go on indefinitely".

US ties with Saudi Arabia 'enduring' despite Syria differences: Kerry

Mr Kerry insisted that US ties with Saudi Arabia are "strategic and enduring", even as the two countries aired their differences.

"Our relationship is strategic, it is enduring and it covers a wide range of issues," Mr Kerry said.

Mr Kerry insisted "there is no difference in our mutually agreed upon goal in Syria" at a joint news conference with Prince Saud.

But Prince Saud, while stressing the strength of ties with the US, slammed the "international community's failure to stop the war against the Syrian people".

He said while the US and Saudi agreed that there must be a handover of power in Syria, there was disagreement over the tactics.

Negotiations to solve any crisis "shouldn't just go on indefinitely", he said in reference to a US-Russian proposed peace conference slated to be held in Geneva later this month.

In a passionate plea, Prince Saud instead called for greater international intervention.

"Syria is being destroyed by carpet bombing. If that is not disregard of human values, I don't know what is," he said.

"If one is choosing a moral choice to intervene or not intervene, what is that choice going to be?

"Do I let this continue or do I help if I can?

"We can't really say that we are taking the high road and establishing our humanity if we let this tragedy continue unabated."

40 per cent of Syrians need humanitarian assistance: UN

Meanwhile, the UN estimates that around 9.3 million people or around 40 per cent of the Syrian population now need humanitarian assistance.

"The humanitarian situation in Syria continues to deteriorate rapidly and inexorably," UN humanitarian chief Valerie Amos told the Security Council behind closed doors, according to her spokeswoman Amanda Pitt.

"The number of people we estimate to be in need of humanitarian assistance in Syria has now risen to some 9.3 million.

"Of them, 6.5 million people are displaced from their homes, within the country."

The population of Syria is about 23 million.

Ms Amos's plea to the council follows the Syrian government's promise to ensure delivery of vaccinations and humanitarian aid across the country, after an outbreak of polio and warnings of malnutrition in areas under military siege.

Twenty-two children in Deir al-Zor province bordering Iraq were left paralysed last month.

The polio virus has been confirmed in 10 of them, with experts warning it could spread quickly across the region.

AFP/Reuters