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More than 70,000 Syrian refugees trapped for months on the border with Jordan are living in "dire" conditions, UN aid chief Stephen O'Brien said Friday.

"The living conditions of the people stranded at the berm are dire," O'Brien told a press conference after visiting makeshift camps for tens of thousands of Syrians who have fled the fighting in their country.

Jordan has since June 21 blocked the refugees from entering the country in addition to preventing aid deliveries to their makeshift camps after a suicide bombing claimed by the Islamic State group killed seven of its soldiers in the desert area.

Since then, humanitarian organisations have been able to send aid to the refugees just once, in early August, lifting the aid across the frontier using drones and cranes.

"There is no access to basic resources such as food and water, with over 75 percent of that population estimated to be women and children," O'Brien said.

"They desperately need assistance and our humanitarian support."

However, he also called Jordan's security concerns "very legitimate", and said discussions were under way with Amman to find a way to deliver aid without endangering the kingdom's security.

O'Brien emphasised the commitment of donor countries to help Jordan ease the burden of the refugee crisis.

The country already hosts more than 600,000 Syrian refugees according to the United Nations, a figure the Jordanians put at 1.4 million.

Amman regularly complains of a lack of international aid, believing it has "reached its limits" and regularly urges the international community to share the responsibility.