The United Nations will convene an international aid conference in Geneva on Sept. 13 to help avert what U.N. Secretary General Antonio Guterres called a "looming humanitarian catastrophe".

"We need the international community to stand together and support the Afghan people," Guterres said in a post on Twitter announcing the conference that he said would seek a swift scale-up in funding for humanitarian relief.

"We also appeal for full and unimpeded humanitarian access to make sure Afghans continue to get the essential services they need," he said.

Many Afghans were struggling to feed their families amid severe drought well before Taliban militants seized power last month and millions may now face starvation with the country isolated and the economy unravelling, aid agencies say.

"The United Nations stands in solidarity with the people of Afghanistan and is committed to staying and delivering for them," Guterres said.