A Palestinian group has pledged to "open the gates of hell" on Israeli if one of its imprisoned members, one accused of plotting a bomb attack against Israelis, dies after being seriously injured during his interrogation. Israel's arrest of 44-year-old Samer Al Arbeed, a suspect it called the leader of a militant PFLP cell, came after the August 23 bombing at a natural spring in the occupied West Bank, killing a 17-year-old Israeli girl and injuring her father and brother. “We hold the Israeli occupation responsible for the lives of the Palestinian prisoner Samer Al Arbeed and his comrades, and we assure that by endangering their lives, the occupation will open the gates of hell,” the military wing of the Popular Front for the Liberation of Palestine said in a statement. The group called on the Palestinian public to attack Israeli soldiers "in support of our valiant prisoners, our soldiers on the front lines". The Israeli military said on Sunday that it had detained at least 27 people in connection with the plot, many of them from the occupied West Bank city of Nablus and the city's Balata refugee camp. The Shin Bet, Israel's domestic security service, left Mr Al Arbeed in critical condition and his lawyers have demanded an international investigation into his treatment. They have specifically asked for the United Nations and the International Red Cross to conduct any probe. Israeli organisations criticised the authorities' conduct. “Israel’s moral image is reflected in the basements of the interrogation cellars of the Shin Bet," said a statement from the Association for Civil Rights in Israel. “Law enforcement agencies are not allowed to torture detainees, whatever their suspicions. Cruel and inhuman means of investigation are categorically prohibited.” Local media reports indicated that Israeli security services were given special measures to interrogate the suspect because of fears of an imminent attack. In order to extract information from the subject, security forces can use tactics such as beatings, sleep deprivation and shackling under the order.