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.

Syria announced that its army had begun to withdraw from violence-hit Sweida on Wednesday, following a wave of Israeli strikes on the capital and a US call for government forces to leave the majority-Druze southern city.

The United States, which is close allies with Israel and has been trying to reboot its relationship with Syria, said an agreement had been reached to restore calm in the area, and urged "all parties to deliver on the commitments they have made".

Israeli troops on Wednesday sought to control crowds and prevent Druze from crossing into Syrian territory, after deadly sectarian violence prompted Damascus to send government forces to Syria's south.

Israeli soldiers in the occupied Golan Heights fired teargas to keep order along the heavily fortified frontier as dozens of people tried to cross over, said an AFP reporter in Majdal Shams, a mainly Druze town in the Israeli-annexed area.

The UN's unflinching expert on Palestinian affairs Francesca Albanese said Tuesday that Washington's sanctions following her criticism of the White House's stance on Gaza are a "violation" of her immunity.

The United Nations' Special Rapporteur on the occupied Palestinian territories made the comments while visiting Bogota, nearly a week after US Secretary of State Marco Rubio announced the sanctions, calling her work "biased and malicious."

"It's a very serious measure. It's unprecedented. And I take it very seriously," Albanese told an audience in the Colombian capital.