UK foreign secretary Jack Straw is being urged to take action over a UK journalist detained in Israel.
Ms Jasiewicz was on an assignment for Red Pepper magazine
Ewa Jasiewicz, 26, was prevented from entering Israel at an airport in Tel Aviv last week and was placed in a detention centre when she appealed.
The Israelis say she is a political activist whose journalism is biased.
The editor of Ms Jasiewicz's magazine Red Pepper has called on Mr Straw to protest in the strongest terms to the Israeli government.
On Friday the Israeli authorities offered to free her on bail, saying that they had no case to hold her.
A friend paid the 30,000 Israeli shekels or £3,600 price.
She was to be freed on condition she did not enter the occupied territories.
Once released Ms Jasiewicz was to appeal these conditions as she was due to go and report on the conditions under which the Palestinian people are living in the occupied territories.
But then the Israeli state appealed against the court's decision to free her and her case is to be heard by the Israeli Supreme Court next week.
Meanwhile Ms Jasiewicz remains in detention.
Her colleagues at Red Pepper suspect Ms Jasiewicz has been singled out because she witnessed and reported on the killing of a 13-year-old Palestinian boy, Baha al-Bahesh, by the Israeli Defence Force soldier in Nablus.
Her eyewitness account of the death received considerable press coverage.
At the time she was a member of the International Solidarity Movement, a Palestinian led organisation which stages protests against the Israeli occupation.
Red Pepper Editor Hilary Wainwright said: "I call on foreign secretary Jack Straw to make the strongest protest to the Israeli government over this outrageous act and to do everything he can to ensure that Ewa is able to do her job and report from Israel and Palestine."
"Ewa has been detained as an act of censorship because the authorities do not want the world to hear what she has to say because she has previously been a witness to crimes committed by the Israeli Defence Force."
The funeral of Baha Al-Bahesh whose death Ms Jasiewicz witnessed
The National Union of Journalists (NUJ) is also urging the British government to intervene.
"Ewa Jasiewicz is a bona fide journalist who has travelled to Israel to research a story.
"She holds an NUJ press card and it is outrageous that she should be treated in this way.
"It is not acceptable that a democratic country should be refused entry to a journalist because they find her work objectionable."
A Foreign and Commonwealth Office spokesman confirmed Ms Jasiewicz was in an Israeli detention centre.
"We are giving her consular assistance which means ensuring she has legal representation and that she is being treated appropriately."
He said that Mr Straw had not taken any action on her case.
He added that issues of press freedom were taken up with various countries but at differing levels of seniority.
A spokesman for the Israeli prime minister told BBC News Online the country had a right to determine who entered it.
"A country has a legitimate right to question the intentions of an individual on entering a country.
"The authorities will behave in accordance with the decision of the court," the spokesman added.
Israel's concern about Ms Jasiewicz related to her links to the International Solidarity Movement, he told BBC News Online.