By Daren Butler

ISTANBUL (Reuters) - When lawyers for Kurdish militant leader Abdullah Ocalan ask to visit him in an island prison south of Istanbul, they are usually told the boat that would ferry them there has broken down.

They have not seen him for more than 15 months, and have not been able to ask Ocalan what he thinks about the hunger strike by hundreds of his supporters in jails across Turkey. But they believe the PKK leader could play a role in ending the protest.

The hunger strike, demanding an end to Ocalan's isolation, is stretching into its third month. Medics say the strikers, some of whom have refused food for 67 days, could soon begin dying. They are consuming sugared water, salt and vitamins.

"Our client is someone who has a serious influence over the Kurds and so we think any call by him to end this protest action could be influential," said Mazlum Dinc, one of Ocalan's lawyers, sitting in cramped offices in central Istanbul.

"But it is really the government who can end this hunger strike," he told Reuters, to nods of approval from his fellow lawyers as they sipped black tea.

Ocalan, the leader of the Kurdistan Workers Party (PKK) militant group, which has been fighting for Kurdish autonomy for almost three decades, has been imprisoned on the small island of Imrali in the Marmara Sea since his capture in 1999.

He has significant support among Kurds but is widely reviled by Turks who hold him responsible for the deaths of over 40,000 people since the PKK - designated a terrorist group by Turkey, the United States and the European Union - took up arms.

The protest by hundreds of Kurdish militants and activists presents a growing challenge for the government of Prime Minister Tayyip Erdogan and risks fuelling tensions in the mainly Kurdish southeast as the protesters' health deteriorates.

One of the hunger strikers in the southeastern city of Diyarbakir was taken to hospital on Saturday with stomach bleeding, although his condition was not thought to be life-threatening.

"In democracies, you don't get rights by using these methods ... I hope they will return from the wrong path. As the government, we won't let anyone die in prison," Erdogan told reporters before leaving on an official visit to Egypt.

He has previously dismissed the protest as "blackmail" supported by "merchants of death".

The hunger strikers have demanded an end to Ocalan's isolation, including access to lawyers, as well as greater Kurdish language rights for Kurds in Turkey, who make up around one fifth of the population.

Seven leading Kurdish politicians joined the protest over the past week, including parliamentarian Leyla Zana, a former Nobel Peace Prize nominee.

LAWYERS IN CUSTODY

Justice Minister Sadullah Ergin has played down reports of Ocalan's isolation, saying his family is able to visit him and that Ocalan himself did not want to talk to his lawyers.

The lawyers reject this and say the authorities have declined their requests to visit him 134 times since they last saw him more on July 27, 2011. They usually cite breakdowns on the boat or bad weather, say the lawyers.

Ocalan's solitary confinement was eased in 2009 when five more inmates were brought to the island. His current situation is unclear but lawyers say he has no access to a telephone or television and his newspapers are censored.

Mehmet Ocalan, the PKK leader's brother, has said he visited him twice in jail in the last 15 months.

Most of Ocalan's lawyers are now on trial accused of links to the PKK, leaving a small group of young, inexperienced colleagues to represent him.

Dinc, 23, was a child when Ocalan was first captured by Turkish special forces in Kenya and brought back to Turkey. He began representing him in August 2011, his first job after university.

His sudden rise to prominence in the law office followed police raids last November in which dozens of Ocalan's lawyers were detained, accused of involvement in an alleged network linked to the PKK.

The lawyers, of which 27 are in custody as the trial continues, are accused of passing on orders from Ocalan to the PKK - a charge they reject.

Fighting between the PKK and Turkish security forces surged over the summer. Ankara linked the renewed hostilities to the conflict in neighboring Syria. Turkey has accused Syrian President Bashar al-Assad of arming the PKK.

Erdogan's government has boosted Kurdish cultural and language rights since taking power a decade ago. But Kurdish politicians are seeking greater political reform, including steps towards autonomy for mainly Kurdish southeastern Turkey.

Addressing one of the protesters' demands, the government has submitted to parliament a bill allowing defendants to use Kurdish in their court testimony. But Kurdish politicians say this alone would not be sufficient to end the hunger strike.

Another of Ocalan's lawyers, Rezan Sarica, said the reform was inadequate as it would only allow for oral defense twice and required defendants to pay for their own translator.

"It will not be enough. It will make a contribution... But the most significant demands of the hunger strikers concern Ocalan," said the 25-year old.

The government is worried about the hunger strike in the light of a similar protest more than a decade ago in which dozens died - both as a result of fasting and a security operation to end the strike.

The justice ministry says around 1,700 people are on hunger strike and doctors were regularly inspecting them. Turkey's largest medical association has warned of fatalities after around 60 days.

(Writing by Daren Butler; Editing by Nick Tattersall and Rosalind Russell)