EU foreign policy chief Catherine Ashton is "following with great concern" the fate of an Islamic Jihad member held by Israel, who has been on a hunger strike since December, a statement said on Saturday.
She is "following with great concern reports about the deteriorating health condition of Khader Adnan," who is being held without charge under so-called administrative detention.
Ashton also requested that the Israeli government "do all it can to preserve the health of Mr Adnan in its continuing handling of this case."
Adnan, a 34-year-old baker, was arrested by Israel on December 17 near the West Bank city of Jenin, where he had been spokesman for Islamic Jihad.
Held since without being charged, he began refusing food a day after his arrest and is now said to be close to death.
The statement said Ashton reiterated the "EU’s longstanding concern about the extensive use by Israel of administrative detention without formal charge. Detainees have the right to be informed about the charges underlying any detention and be subject to a fair trial."
Under Israeli law, a military tribunal can order an individual held without charge for up to six months at a time. Such orders can be extended by further six-month periods indefinitely, if approved in a new court session.
Following a recent examination of the prisoner, an Israeli NGO on Wednesday expressed grave concern about his well-being.
"Khader Adnan is in immediate danger of death," Physicians for Human Rights-Israel said of the man, who completed 62 days on strike on Friday.
"A fast in excess of 70 days does not permit survival," it said. "Infusion of liquids, adjustment of salts and the addition of glucose and vitamins cannot prevent certain death."
Human rights groups in Israel and overseas have appealed to Israel to free Adnan or put him on trial.