“Any Palestinian government must unambiguously and explicitly commit to nonviolence, recognition of the state of Israel, and acceptance of previous agreements and obligations between the parties,” Ms. Psaki said, citing conditions Hamas has repeatedly rejected. “It’s hard to see how Israel can be expected to negotiate with a government that does not believe in its right to exist.”

Hamas and Fatah, the faction that dominates the P.L.O., have signed several similar accords before that were not carried out, so it remained unclear whether Wednesday’s deal promised a real resolution or a replay of an old movie.

Some analysts saw the step primarily as a tactic by President Mahmoud Abbas of the Palestinian Authority to pressure Israel to make concessions as the clock winds down on extending the fraught negotiations. He said in statement that “there is no contradiction at all” between reconciliation and negotiation, adding, “We are totally committed to establishing a just and comprehensive peace based on the two-state principle.”

Other experts noted that Palestinian political conditions have drastically changed since the signing of previous agreements, which could lead both parties to make the compromises necessary to put this one into action. Hamas has been in a deep political and economic crisis since the military-backed government took over Egypt last summer and largely cut ties with Gaza. Mr. Abbas, at 79, is looking for a legacy and an exit strategy.

Reconciliation is deeply resonant among Palestinians and could revive the president’s sagging popularity.