In his letter, Abbas warns that Hamas' refusal to recognize Israel undermine "diplomatic achievements," provides Israel with an excuse for refusing to negotiate with the Palestinians, and would affect foreign aid to the PA, the Guardian reported.
However, the letter was also meant to warn western countries against cutting off aid to the Palestinians, a source close to Abbas said.
"To avoid the perception they (Hamas) fail because of a foreign conspiracy we need the world to show that it is still willing to support the moderate line and not just cut us off," the source said.
Abbas to set up new border crossings agency
Earlier, Palestinian negotiator Saeb Erekat said a Palestinian investment fund that controls hundreds of millions of dollars will remain under Abbas' control in a bid to prevent Hamas access to the money.
Abbas also plans to set up a new presidential agency that would exercise control over border crossings between the Palestinians and Israel, Erekat said, adding he has been designated as the agency's director and that the new body would aim to resolve any disputes with Israel in order to ensure the crossings remain open.
The latest moves mark further Abbas attempts to consolidate his power ahead of the formation of the new Hamas led government.
Abbas and Hamas appear to be headed for confrontation over the Islamic group's insistence to form a new government based on some principles rejected by the Palestinian leader.
Earlier this week, Hamas challenged Abbas by insisting on forming the government before the upcoming Israeli elections, despite a series of objections voiced by the PLO to Hamas' government principles.
Hamas members denied they were interested in a confrontation, but a senior Palestinian official told Ynet the PA was nearing a 'political and legal crisis.'