RAMALLAH, West Bank (AP) - Palestinian rivals Hamas and Fatah on Monday were locked in a new dispute that threatens to derail next week’s Fatah convention, seen as key to rehabilitating the corruption-stained party that has led peace talks with Israel.

Officials in Hamas-ruled Gaza said Monday they would only allow Fatah delegates to leave the territory and travel to the conference if Fatah’s leader, Palestinian President Mahmoud Abbas, releases hundreds of Hamas detainees in the West Bank, where his Western-backed Palestinian Authority is based.

The convention, Fatah’s first in 20 years, is to convene in the West Bank town of Bethlehem. More than 1,500 delegates, nearly one-third of them from Gaza and the rest from the West Bank and the Palestinian diaspora, are to choose dozens of new leaders and vote for a fresh political program.

The convention is seen as crucial to Fatah’s attempt to clean up its image, tainted by petty infighting and corruption, and present itself as an alternative to the militant Islamic Hamas. A stinging loss to Hamas in a 2006 parliamentary election and failure to establish a Palestinian state through negotiations with Israel have increasingly demoralized the once dominant party .

Abbas aides were not immediately available for comment on the standoff with Hamas, but a senior Palestinian official said Abbas had asked Syria, Russia and Turkey to intervene and help soften Hamas’ demands. The official spoke on condition of anonymity because he was not authorized to discuss the behind-the-scenes negotiations.

Nabil Shaath, a Fatah leader, said Monday it appeared unlikely the convention would be held without the Gaza contingent. "There would be a massive boycott of the conference " in such a case, he said in an interview.

Shaath, who has been involved in Egyptian-brokered reconciliation talks between Hamas and Fatah, said his own movement had mishandled the prisoner issue and that its attempt to get foreign mediators to pressure Hamas on the subject was doomed to failure from the start.