UN aid chief Valerie Amos said Thursday she was still pushing Damascus to allow international aid organisations to operate in Syria, warning that more than one million Syrians faced "destitution".

"Over a million people have been uprooted and face destitution. Perhaps a million more have urgent humanitarian needs due to the widening impact of the crisis on the economy and people's livelihoods," she told reporters in Damascus.

Amos said UN agencies in Syria and their local partners could not handle the humanitarian crisis alone and that she would continue to lobby the government to allow in more aid workers and organisations.

"What I would like to see is the government extending that facility to other large NGOs from the international community who we know can really help to scale up the efforts significantly.

"I have not been able to get that agreed," she said.

Damascus has dragged its heels in the past at the prospect of allowing non-governmental organisations into the country, which has been convulsed by an escalating conflict since March 2011.

"The government has a concern that the assistance will reach, in their terms, armed groups or terrorists. This issue was raised with me in every single conversation that I had with a government minister," Amos said.

"I continue to lobby the government to be more flexible in its approach to humanitarian operations. There is no reason why ordinary Syrians should not receive as much help as is practically possible."

A Syrian watchdog says more than 23,000 people have died since the uprising against the regime of President Bashar al-Assad erupted, while the UN puts the toll at around 17,000.

Apart from those displaced within Syria, the UN says at least 157,600 people have fled to neighbouring countries, based on those registered, while residents of conflict zones are suffering shortages of food, power and medical supplies.