The exit of foreigners from Gaza via the Rafah border crossing has been halted in an apparent dispute over evacuating injured patients.
Hundreds of foreign citizens have escaped through the crossing into Egypt in the past few days.
But on Saturday, no foreign nationals, dual nationals or injured patients were let through, Palestinian sources said.
Hundreds of people with foreign passports went to the border, but the gate did not open.
Sources from the crossing authorities on the Palestinian side told the BBC that movement of people with foreign passports is not being allowed until there is agreement on the safety of transferring injured patients.
There has been no official statement from the authorities as yet.
The UK Foreign Office confirmed that British citizens in Gaza had been unable to leave via the Rafah crossing.
A spokesperson told the BBC: "We are disappointed that the Rafah crossing has been temporarily closed today.
"This continues to be a complex and challenging situation and we are using all diplomatic channels to press for its reopening in coordination with our international partners."
The Rafah border crossing between Gaza and Egypt opened on Wednesday to allow a number of civilians to leave Gaza.
It was their first opportunity to do so since the war began on 7 October, when Hamas gunmen staged an unprecedented assault on southern Israel that killed more than 1,400 people.