An adviser to the Palestinian president says Mahmoud Abbas' Fatah movement wants him to stick to long-standing demands for resuming talks with Israel.

Wednesday's remarks cast new doubt over an upcoming U.S. peace mission. Secretary of State John Kerry is expected in the region next week to try to restart Israeli-Palestinian negotiations, which broke off in 2008.

Abbas has said he can't negotiate unless Israel stops building in settlements on war-won lands or accepts its 1967 frontier as a starting point for border talks — territory before the capture of the West Bank, Gaza Strip and east Jerusalem.

Israel has rejected the demands.

Abbas' adviser Nabil Abu Rdeneh says that Fatah rejects attempts to pressure the leader to drop his demands, an apparent reference to the U.S. initiative.