The US secretary of state says she will be returning soon to the Middle East to support Israel-Palestinian peace talks.
The three held a brief photo call but did not speak to the media
Condoleezza Rice was speaking after her first joint meeting with the Israeli and Palestinian leaders in Jerusalem.
Ms Rice reported no tangible progress at the rare summit, except to say that the leaders agreed to meet again soon.
Palestinian Authority President Abbas has recently agreed a power sharing deal with the ruling Hamas movement which is sworn to Israel's destruction.
The deal earlier this month between Hamas and Mr Abbas's Fatah movement ended weeks of internal fighting that has cost more than 90 lives.
Mr Olmert said on Sunday that US President George W Bush had privately promised Washington would join Israel in shunning any government including Hamas.
But Ms Rice said the US would reserve judgement until the proposed national unity government had been formed.
The summit in a luxury West Jerusalem hotel began with Mr Abbas, Mr Olmert and Ms Rice exchanging polite smiles and shaking hands, before they sat round a small table.
The three were alone, without aides, accompanied only by Ms Rice's Arabic interpreter.
After about an hour, they moved to Ms Rice's suite overlooking the Old City, in East Jerusalem.
Some 90 minutes later, Ms Rice appeared alone to give a brief statement issued in the name of the three parties.
"The president and [Israeli] Prime Minister [Ehud Olmert] agreed that they would meet together again soon," Ms Rice said.
"They reiterated their desire for American participation and leadership in facilitating efforts to overcome obstacles, rally regional and international support and move forward toward peace."
"In that vein I expect to return to the region soon," she said, without taking questions.
Neither the Israeli nor Palestinian leaderships were available for further comment, although a Hamas representative branded the summit a failure.
"Rice did not succeed in pressuring President Abbas to withdraw from the unity government.
"We call on the US administration to respect the Palestinian people's will and recognise the [Hamas-led] government and open a dialogue," said spokesman Ismail Radwan.
Monday's meeting - billed last month as the launch of a new US initiative to revive Israeli-Palestinian peace negotiations - has been eclipsed by the Fatah-Hamas agreement signed in Mecca earlier in February.
Palestinian Prime Minister Ismail Haniya of Hamas now has five weeks to get a new cabinet accepted by the Hamas-dominated parliament.
The US and Israel have stressed that any future Palestinian administration must recognise Israel, renounce violence and commit to previous agreements between the Palestinian Authority and Israel.
Hamas has agreed to "respect" past peace agreements, but says it is not ready to alter its fundamentally anti-Israeli philosophy.
The diplomatic isolation of the Hamas-led government and its economic boycott by Israel and western countries have been accompanied by a drastic decline in living standards in the Palestinian territories and deadly inter-factional violence.
Palestinians were infuriated on Sunday when Mr Olmert appeared to prejudge the outcome of their unity deal, saying that President Bush had already agreed to boycott the government unless Hamas recognises Israel and renounces violence.
The last Israeli-Palestinian summit attended by a top US official took place in 2003, chaired by Ms Rice's predecessor Colin Powell.