Hamas Prime Minister Ismail Haniyeh sent a letter to Abbas on Friday urging him not to hold the vote and to continue negotiations over the plan. He said the referendum would divide the Palestinian people and instead proposed forming a national unity government with Fatah. "The idea of the referendum now on the table carries many dangers," Haniyeh wrote. "I'm afraid it will cause a historic rift that will hurt the Palestinian cause for decades to come." PA Chairman Mahmoud Abbas is expected Saturday to formally announce a July 31 date for a national referendum on establishing a Palestinian state along the 1967 borderline. Fatah leader Marwan Barghouti, currently imprisoned in Israel, has recently been in contact with Hamas leader-in-exile Khaled Mashaal in an attempt to find a solution to the conflict raging over the prisoners document. According to Army Radio, the Arabic-language paper Asharq al-Awsat reported that Mashaal Barghouti through Barghouti's wife Fadwah and requested certain changes to the prisoners initiative. PA Chairman Mahmoud Abbas was reported to be satisfied with the compromise reached by Barghouti and Mashaal. Meanwhile, Abbas canceled a planned visit to Indonesia just hours after the trip was announced, an Indonesian foreign ministry spokesman said Friday. Abbas, who was to have arrived June 23 to discuss the Middle East peace process with his territory's longtime ally, apparently decided it wasn't a good time to be away. "The visit was canceled because of (the Palestinian) domestic situation," ministry spokesman Desra Percaya said. Abbas also had intended to discuss plans to hold a national referendum on establishing a Palestinian state alongside Israel and brief his Indonesian counterpart, Susilo Bambang Yudhoyono, on broader peace initiatives, Percaya said. Indonesia, the world's most populous Muslim country, has long supported Palestinian independence efforts and is considering opening a diplomatic mission in the West Bank town of Ramallah.