GAZA, June 5 (Nidal al-Mughrabi/Reuters) - Palestinian footballer Mahmoud Al-Sarsak left the Gaza Strip in the summer of 2009 to play football in the West Bank. But he never reached his goal.

He was arrested by Israeli security and, after three years of detention without trial, Sarsak is on hunger strike.

His current term of detention term ends on August 22 but there is no guarantee that it will not be renewed for a further six months, as it has been before, his family and lawyer said.

The entire family and friends are afraid for Mahmoud's life and the worry is killing us, said Sarsak's older brother, Emad.

The 25-year-old is in an Israeli jail on secret charges that he is an unlawful combatant linked to the militant group Islamic Jihad, an allegation he denies.

Sarsak had joined the local football team in his Rafah refugee camp in the southern Gaza Strip at 14, becoming the youngest footballer to play in the Palestine Liga A at the time. The midfielder attracted the attention of a German coach while playing for the Palestine national team in Norway.

He always dreamed of playing outside the country, to represent Palestine through playing for an Arab or an international team, and he was talented enough, Emad said.

The first step was to play for a team in the West Bank. But Israeli security arrested him on July 22, 2009, at the Erez crossing from the blockaded Gaza enclave, the only route to Palestinian territory in the occupied West Bank.

Mahmoud would not have tried to cross through Erez if he had anything to fear. He belonged to no (militant) faction and he had done nothing wrong, Emad, 36, told Reuters.

Mahmoud began his strike on March 15, demanding an end to his unjustified detention.

The prisoner has been on an intermittent hunger strike and is receiving medical care in a Prisons Service medical facility, Israel's Prison Service said in a statement in response to queries. As in the past, he will be transferred to hospital as required.

On May 14, Israel struck an agreement with representatives of 1,600 Palestinian prisoners to end a 27-day hunger strike, agreeing to stop solitary confinements, allow family visits and improve detention conditions.

But it did not promise to end administrative detention, a practice whereby secret information can put a person in jail for months or years. It did, though, agree that future extension of such terms would require a court order and list of charges.

It seemed the Israelis cheated and the Egyptians (mediators) did not deal with Mahmoud as an administrative detainee. So Mahmoud pursued his hunger strike demanding his freedom, said the brother, a civil servant in Gaza.

NO TRIAL

Lawyer Mohammed Jabarin said Israel introduced the law allowing it to detain unlawful combatants without trial following its withdrawal from Gaza in 2005.

The danger of such a law is that as long as Israel sees the situation as a war situation it allows itself to keep some people in prison. It is more serious than administrative detention, he told Reuters by phone.

He said Sarsak had lost at least 10 kgs (22 pounds) and recently began having injections and solutions of salt to combat pain, weakness and deteriorating eyesight.

Jabarin said there were talks with the Israeli prison authorities over Sarsak's hunger strike but there was no official promise by Israel it would not renew his detention.

He said Israel's security holds Sarsak on suspicion of having ties with the Islamic Jihad group, but had failed to make formal charges.

The Sarsak family wants Palestinian factions and leaders to show more public support for Mahmoud.

Standing by Mahmoud is a national duty. The family urges leaders and human rights groups to pressure Israel to release our son whose life is in danger at the moment, Emad said.

Sport was everything he admired and embraced in life, said his mother. We miss him every moment, every time we gather for a meal or to drink tea. I urge him to pursue his strike and remain steadfast until they meet his demands. (Additional reporting by Dan Williams and Noah Browning. Editing by Douglas Hamilton and Robert Woodward)