United Nations aid trucks have crossed from Turkey into Syria for the first time in three years, a development aid officials hope will lead to greater humanitarian access to civilians hardest hit by the civil war.

But with the convoy heading to a region controlled by forces loyal to President Bashar al-Assad, doubts remained whether those in rebel-held areas most urgently in need would benefit.

The trucks travelled through the largely deserted frontier at the Nusaybin border post, taking food supplies, bedding and medicine towards the ethnic Kurdish city of Qamishli in Syria.

It is the first time in three years of this brutal conflict that the UN has been able to carry aid across into Syria from Turkey

Nigel Fisher, UN regional humanitarian coordinator

"It is the first time in three years of this brutal conflict that the UN has been able to carry aid across into Syria from Turkey," Nigel Fisher, the United Nations' regional humanitarian coordinator, said in a statement.

The convoy became possible after the UN Security Council last month unanimously called on Syrian authorities and rebels to allow humanitarian supplies across front lines and borders by the most direct routes, to reach an estimated 9.3 million people in need.

Western aid officials say the joint effort by agencies including the World Food Programme (WFP), children's agency UNICEF and the World Health Organisation (WHO) is a step towards alleviating suffering in a conflict that has already claimed the lives of 140,000 people, although they privately express concerns that the worst affected will still not be helped.

Small crowds gathered at the Nusaybin frontier as the convoy crossed, containing supplies for more than 50,000 people.

A Syrian government flag was fluttering on the other side of the border as the trucks got under way, with the aid due to be distributed by partners of the regime as stipulated by Damascus, sources said.

A spokeswoman for WFP said that the organisation was working out a delivery plan "aiming to get the food to both sides of the conflict".

Abeer Etefa said that up until now WFP had resorted to hugely expensive and limited air drops to reach 200,000 needy people in Hasakah governorate, where the trucks are headed.

"We hope that in the future this becomes a way to get food to desperate families," she told the Reuters news agency.

Source: Agencies