But it continued to back the Israeli stance that President Yasir Arafat was not an acceptable counterpart in negotiations to end the Israeli-Palestinian conflict.
White House spokesman Scott McClellan said US officials were reaching out to their Israeli and Palestinian counterparts, and urged all parties to "consider carefully the consequences of their actions" for the US-backed plan known as the road map.
"We remain committed to implementation of the road map, working with Israelis, Palestinians, Arab States who seek peace," as well as the diplomatic "quartet" that crafted the peace plan, said McClellan in a statement released hours after Arafat accepted Abbas' resignation.
That group includes the European Union, the United Nations, Russia, and the United States, which had made Abbas' appointment a precondition for releasing the blueprint and moving towards the creation of a Palestinian state.
"The creation of the office of prime minister was a key turning point for the Palestinian Authority in the development of new institutions to serve all the people, not just a corrupt few tainted by terror," he said.
Hopes on Abbas
US President George Bush had pinned much of Washington's hopes on Abbas, even welcoming him to the White House on July 25 after steadfastly refusing to sit down with, or even talk to, Arafat.
And McClellan insisted the Palestinians had to battle anti-Israeli violence, saying: "The prime minister must be supported by a cabinet committed to fighting terror, political reform, and rooting out corruption."
Arafat said Abbas would head up a caretaker government for the next five weeks, after which he would either be asked to form a new government or his replacement will be appointed.
Arafat (L) appears to have won
a power struggle with Abbas
Acknowledging that Abbas' resignation clouded the way forward, US Homeland Security chief Tom Ridge said on the sidelines of an international forum in Cernobbio, Italy that the move "will cause inevitable delays" .
"There was great promise there, great hope there," he said. "We will have to see who will succeed him, but for the United States, Arafat is not a partner because he has not participated in the peace process as he should have."
EU decision welcomed
However, Ridge - a close Bush adviser - said the US leader would not abandon efforts to bring the parties to the negotiating table "to recommence discussions and to respect" the steps laid out by the road map.
Separately, US State Department Richard Boucher welcomed a decision by the European Union foreign ministers to blacklist the political wing of the radical Palestinian group Hamas.
"This is an important step," he said in a statement. "We look for the EU to carry through with the political decision it reached today and to take action against Hamas on an urgent basis."
The EU decision, which Washington had pushed strongly, coincided with a Hamas vow to avenge a failed assassination attempt by Israel against its spiritual leader, Sheikh Ahmad Yassin.