"They have made it clear I won't be admitted to Israel," Lauren Booth told Agence France-Presse (AFP) on Wednesday, September 3.
"When I went to the Israeli checkpoint I was threatened with being shot four times," she said.
Israeli authorities have turned down a request from Booth, a journalist and human rights activist, to leave the Gaza Strip through the Erez crossing with Israel.
"There is no possibility to let in those people who entered by the sea. They cannot enter Israel," said spokesman Peter Lerner.
Booth arrived to Gaza by sea on August 23, along with 43 foreign activists in a bid to break the month-long Israeli siege.
All activists left last week to Cyprus by sea, except nine, including Booth, who decided to stay longer.
Booth and two other activists have also been denied exit through the Rafah border crossing by Egypt.
"When I went to the Rafah crossing (into Egypt) I had all the permission lined up at the top level but a lowly official stopped me from leaving," she recalls.
"We were all turned back by the Egyptians," said Booth, adding suggesting Egypt "was under pressure from Israel to act that way."
Booth said her ordeal is giving her a first-hand experience of what Palestinians have been living with for months.
"This is a real Palestinian experience of being between the devil and the deep blue sea," she told AFP.
"I'd actually like to say 'thank you very much' to the Israeli authorities at Erez for giving me this fantastic chance to feel just exactly what it is like to be inside what is effectively the world's largest internment camp, where individuals who should have the right to travel under international law are withheld in a 40 kilometer by 10 kilometer camp," the British activist told the BBC.
"Thanks to Israel for letting us feel a real taste of Gazan life."
Israel has been closing the Gaza Strip's exits to the outside world for long months, banning food, fuel and medical supplies.
Money and in kind assistance raised by NGOs and individuals remain stranded at the Egyptian border with Gaza, the latest being a Scottish aid convoy.
"I am effectively being imprisoned here by authorities who wish to punish human rights activists who have come to view the situation in Gaza," said Booth.
She will not request help from her brother-in-law Blair, who the Quartet's special envoy to the Middle East.
Booth, rather, urged Blair, currently visiting Israel, to focus on the Palestinians and "the terrible poverty entirely created by the siege."
"It is his duty as Middle East envoy to make sure he makes the effort to come here."