In Syria's Druze-majority city of Sweida, residents said they have been living in terror since the arrival of government forces who have been carrying out what witnesses and a war monitor have called summary executions.

"A lot of my friends were killed, including a doctor who was going to hospital," said Osama, 32, by telephone on Wednesday, adding he was in the centre of the southern city.

"There were summary executions in the streets," he told AFP crying, declining to provide his surname.

A crush at an aid centre in southern Gaza killed at least 20 people on Wednesday, with the site's operator blaming "Hamas operatives" within the crowd and the Palestinian territory's civil defence agency attributing the panic to Israeli gunfire.

It was the first time that the Gaza Humanitarian Foundation (GHF), backed by the United States and Israel, acknowledged deaths at one of its distribution sites after weeks of chaotic scenes and near-daily reports of Palestinians being killed nearby while waiting to collect rations.