Palestinian President Mahmoud Abbas said Sunday that he is determined to form a power-sharing government with his Hamas rivals, despite their deep differences.

Abbas comments come a day after Palestinian Prime Minister Salam Fayyad submitted his resignation. The move is meant to ease the formation of a new caretaker government to oversee new elections.

In the West Bank city of Ramallah on Sunday, Abbas said any new government must accept previous Palestinian obligations. That includes recognizing Israel, which Hamas refuses to do.

The United States will only recognize a future Palestinian unity government if Salem Fayyad is reappointed prime minister, according to a message relayed by Secretary of State Hillary Clinton to European and Arab leaders at last week's donor summit in the Egyptian resort town of Sharm el-Sheikh. The same message was relayed to Hamas by the Norwegian government, in response to the organization's demand that Fatah replaces Fayyad with an independent candidate.

Senior Palestinian sources Saturday told Haaretz that the sudden resignation of Fayyad was a tactical move, designed to pressure Hamas into softening its opposition to Fayyad serving as prime minister in a unity government. The sources believe that the American threat, which is likely to be backed by the European Union and Egypt, will lead to Hamas changing its position and Fayyad rescinding his resignation. It is also feasible that the continuation of Fayyad's term as Palestinian prime minister will be on the agenda during talks between the U.S. and Syria, where the head of Hamas' political wing resides.

Western diplomats confirmed over the weekend that Washington has relayed messages to Hamas, via a European country that is in contact with the organization. The message intimated that a future unity government in the Palestinian Authority must be composed of technocrats who are members of neither Hamas nor Fatah, apart from Fayyad.