Palestinian leaders are "seriously considering" a one-state solution with Israel as progress in peace negotiations continue to stall, former U.S president Jimmy Carter wrote in a Washington Post op-ed published on Sunday.

"Many Palestinian leaders are seriously considering acceptance of one state, between the Jordan River and the Mediterranean Sea," Carter wrote.

"By renouncing the dream of an independent Palestine, they would become fellow citizens with their Jewish neighbors and then demand equal rights within a democracy," he added.

Over the past 16 months Carter has made several excursions to the Middle East with the "Elders Group" - a delegation comprising veteran world leaders including Archbishop Desmond Tutu, former presidents Fernando Henrique Cardoso of Brazil and Mary Robinson of Ireland, former Prime Minister Gro Brundtland of Norway and women's activist Ela Bhatt of India.

"Three of us had previously visited Gaza, which is now a walled-in ghetto inhabited by 1.6 million Palestinians, 1.1 million of whom are refugees from Israel and the West Bank and receive basic humanitarian assistance from the United Nations Relief and Works Agency," Carter wrote in his op-ed.

During the visits, the elders met with prominent figures from Israel, Egypt, Lebanon, Saudi Arabia, Jordan, Syria, the West Bank and Gaza.

"Increasingly, desperate Palestinians see little prospect of their plight being alleviated," wrote Carter in reference to surveying towns in Gaza. "Political, business and academic leaders are making contingency plans should President Obama's efforts fail."

Carter was in Damscus when President Obama made his speech in Cairo and said the speech "raised high hopes among the more-optimistic Israelis and Palestinians, who recognize that his insistence on a total freeze of settlement expansion is the key to any acceptable peace agreement or any positive responses toward Israel from Arab nations."

Carter also wrote in his op-ed that Palestinian Prime Minister Salam Fayyad was committed to his plan for a unilateral declaration of a de-facto Palestinian state, regardless of process in peace negotiations.