* Palestinians and Egyptians seek prisoners' release
* World powers express concern
* Gaza militants say any deaths would undermine calm (Adds comments from the U.N. Secretary-General, paragraph 13)
By Noah Browning
RAMALLAH, West Bank, Feb 19 (Reuters) - Hundreds of Palestinian prisoners in Israeli jails declared a one-day fast on Tuesday in solidarity with four inmates whose hunger strike has fuelled anti-Israel protests in the occupied West Bank.
Samer al-Issawi, one of the four Palestinians who have been on hunger strike, has been refusing food, intermittently, for more than 200 days. His lawyer says his health has deteriorated.
Gaunt and using a wheelchair, Issawi appeared on Tuesday before a Jerusalem civil court, which deferred releasing him for at least another month.
The prisoners' campaign for better conditions and against detention without trial has touched off violent protests over the past several weeks outside an Israeli military prison and in West Bank towns.
In the Gaza Strip, the Islamic Jihad group said a truce with Israel that ended eight days of fighting in November could unravel if any hunger striker died.
The Palestinian Prisoners Club, which looks after the welfare of inmates and their families, said 800 prisoners were taking part in the daylong fast.
Issawi was among 1,027 jailed Palestinians freed by Israel in 2011 in exchange for Gilad Shalit, a soldier who was abducted on the Gaza border by Hamas, the Islamist militant group that now rules the enclave.
Issawi and Ayman Sharawneh, who has also been on hunger strike, are among 14 Palestinians who have been re-arrested by Israel since being released in the Shalit trade.
Ofir Gendelman, a spokesman for Israeli Prime Minister Benjamin Netanyahu, wrote on Twitter that Issawi and Sharawneh were detained "because they violated the terms of the Shalit deal by returning to illegal activities which pose a threat."
Palestinian negotiator Saeb Erekat said he had been in contact with Israel and urged it to release the men. He said Egypt, which helped mediate the Shalit prisoner swap and also negotiated an end to a Palestinian mass hunger strike in Israeli jails last year, was trying to end the new protest.
Israel has defused previous long-term hunger strikes among the some 4,700 Palestinians in its jails by agreeing to release individuals or deporting them to Gaza - a prospect rejected by the four prisoners, who come from Jerusalem and the West Bank.
The Quartet of Middle East negotiators - the United States, Russia, the United Nations and European Union - and U.N. Secretary-General Ban Ki-moon have expressed concern at the hunger strike.
Ban said on Tuesday that he had raised his concerns in a recent phone call with Netanyahu and that "those detained should be charged and face trial with judicial guarantees in accordance with international standards, or be promptly released."
In a statement on Monday, France's Foreign Ministry urged Israel "to be sensitive to the risk of a tragic outcome and to take appropriate measures as a matter of urgency."
The statement said "administrative detention must remain an exceptional measure of limited duration and be carried out with due regard for fundamental safeguards."
Israel holds some Palestinians in "administrative detention" based on evidence presented in a closed military court. It says the practice pre-empts militant attacks against it while keeping its counter-intelligence sources and tactics secret.
There were 178 administrative detainees in Israeli jails in January, down from just over 300 around the time of another Palestinian hunger strike campaign last spring, according to Palestinian rights group Addameer.
"The battle waged by me and by my heroic colleagues ... is everyone's battle, the battle of the Palestinian people against the occupation and its prisons," Issawi said in a message conveyed to the Palestinian Ministry of Prisoners last week. (Additional reporting by Nidal al-Mughrabi in Gaza, Ali Sawafta in Ramallah and Michelle Nichols at the United Nations; Editing by Alison Williams and Doina Chiacu)