Former US President Jimmy Carter has urged Israel and the US not to punish the Palestinians for giving Hamas a victory in parliamentary elections.
Mr Carter's organisation helped declare polling free and fair
The two allies have already taken steps to withhold funds from a government led by the militant Islamist group, which they brand a terror organisation.
"The likely results will be to alienate oppressed and innocent Palestinians," Mr Carter wrote in a US newspaper.
Hamas took 74 out of 132 seats in polls for parliament in January.
Hamas leaders are set to begin talks on the composition and programme of the new Palestinian government later on Monday.
Officials from the group will meet Palestinian Authority President Mahmoud Abbas and representatives from other parties.
Mr Carter's human rights organisation was one of a number of groups that monitored the poll. As president in the 1970s he worked on the breakthrough Camp David accords - the first peace treaty between Israel and an Arab country, Egypt.
Mr Carter's article in the Washington Post argues that despite the Hamas success, Mr Abbas retains considerable constitutional control in the political and security spheres.
He is also optimistic that Hamas will appoint moderates or technocrats to the cabinet and prime ministership and focus its influence on the legislature.
Turning to Israel and the United States, Mr Carter demands that they play positive roles during this fluid period in Palestinian politics.
"Any tacit or formal collusion between the two powers to disrupt the process by punishing the Palestinian people could be counterproductive and have devastating consequences," he says.
Mr Carter says Mr Abbas retains strong powers despite Hamas' win
"Unfortunately, these steps are already underway."
Israel has moved to withhold about $50m per month paid to the PA in customs and tax revenues.
It is also determined to hinder movement of elected Hamas MPs through the 100-plus military checkpoints it maintains in the occupied West Bank.
US officials meanwhile have announced that all its funding for the new government will be withheld, including money that would go to pay schoolteachers, police and hospital staff.
Mr Carter criticises Washington for not agreeing to bypass the government and allow funds be channelled through NGOs.
Punishing ordinary Palestinians will increase alienation, incite violence and - far from inducing Hamas to moderate its anti-Israel stance - will actually increase its influence and reputation, Mr Carter argues.
He also indirectly criticises Israel for avoiding peace talks not just with Hamas, but with past leaders who did recognise Israel's right to exist.
"The election of Hamas candidates cannot adversely affect genuine peace talks, since such talks have been non-existent for over five years," he writes.
But if Israel is willing to include the Palestinians, he argues, Mr Abbas could still play the negotiating role - as Yasser Arafat did before him - in his role of leader of the Palestine Liberation Organisation.