GAZA CITY, August 3, 2008 (AFP) - Israel began sending Fatah members who had fled deadly clashes in the Gaza Strip back to the territory on Sunday at the request of Palestinian president Mahmud Abbas, Israeli security officials said.

Those crossing back into the Gaza Strip were detained for questioning by the Hamas-run security forces, a Hamas official said.

Abbas had asked Israel to allow some 180 people to leave Gaza after 11 people were killed in clashes on Saturday with Hamas gunmen in the deadliest internal fighting since the Islamists seized power in June 2007.

'Yesterday evening Abu Mazen (Abbas) and (Palestinian prime minister Salam) Fayyad made a request for Israel to allow them to cross into Israel and then to hospitals and the West Bank,' a senior Israeli official told AFP.

'Shortly afterwards (Israeli Defence Minister Ehud) Barak was contacted again by Abbas who asked him to allow all of them to return to Gaza,' the official said on condition of anonymity.

Another security official said the decision was taken by Abbas following 'assurances given from a foreign party' -- a reference to Egypt which has brokered indirect negotiations between the rival Palestinian factions.

Spokesmen for Abbas, who was in Jordan, could not be reached for comment.

By Sunday afternoon, 32 people had been sent back, and the remainder of those who fled were expected to be returned later in the day, officials said.

More than 20 people who were evacuated from Gaza and hospitalised for wounds inflicted in the fighting will remain in Israel until they recover.

The Fatah supporters had fled Gaza on Saturday after 11 people were killed and more than 100 wounded in clashes between Hamas-run security forces and the pro-Fatah Helis clan, according to three Gaza-based human rights groups, who updated a previous toll.

The groups indentified those killed as eight members of the Helis family, two Hamas gunmen and a man killed in the crossfire.

The clashes followed a week in which the Islamist movement cracked down on its rivals in Abbas's Fatah party, detaining upwards of 300 people.

Tensions have been high in the impoverished coastal strip of 1.5 million people since Hamas blamed Fatah for a beachside bombing more than a week ago that killed five senior Hamas militants and a little girl.

On Saturday Hamas accused members of the Helis clan over the attack.

Hamas spokesman Sami Abu Zuhri said on Sunday said Hamas-run security forces had received 'dozens' of returnees and detained them for questioning, denying there were any political motives at work.

'Those who are accused of breaking the law will be investigated and if they are found to be guilty will be brought to justice. Those who are proved innocent will be released,' Abu Zuhri told AFP.

He had earlier said the decision of the Fatah supporters to flee 'confirms these people are breaking the law, because they prefer to surrender themselves to the (Israeli) occupation than to stay in their homes.'

Fatah denied any involvement in the beach bomb, but in an apparent tit-for-tat arrest campaign Abbas's security forces detained dozens of Hamas members in the Israeli-occupied West Bank over the past week.

The Arab League on Sunday called on both sides to halt the violence.

'What is taking place is causing unimaginable harm to the Palestinian cause,' Assistant Secretary General for Palestinian affairs Mohammed Sobeih told reporters in Cairo.

Following requests from Egypt and Abbas Israel, which has been holding US-backed peace talks with the Palestinian leader since November, initially allowed the Fatah members to leave Gaza despite a months-old blockade.

'Our position in principle is that we work with and aid those among the Palestinians who struggle against radical Islam, who oppose terrorism, and who favour negotiations,' Deputy Prime Minister Haim Ramon told army radio.

Since Hamas seized power in Gaza Israel has sealed the territory off from all but limited humanitarian aid as Palestinian militants have launched hundreds of rocket and mortar attacks on southern Israel.

The fighting came to a virtual halt on June 19, however, when Israel and Palestinian militants entered into an Egyptian-brokered truce.