Palestinians have said Abbas made no such promises, committing only to do his best to work for the soldier's release.
Western demands
The statements came ahead of separate meetings between Condoleezza Rice, the US secretary of state, and both Olmert and Abbas on Sunday during four days of shuttle diplomacy aimed at restarting the dormant Middle East peace process.
Olmert said any talks would likely be complicated by the programme of the Palestinian unity government.
"The platform of the unity government - the legimitisation of armed resistance, the violation of commitments by the president - all this won't make contacts any easier in the future," Olmert said.
The unity cabinet has stopped short of agreeing to Western demands of renouncing violence, recognising Israel and agreeing to abide by past peace deals.
Ismail Haniya, the prime minister, has said the new government will respect past peace accords, but he has also insisted on the Palestinians' right to resist Israeli occupation.
Israel is continuing to boycott the new government.
The US and other countries are boycotting its Hamas members, instead maintaining contact with independents and Fatah representatives.
UN visit
The Israeli accusations came on the same day as a flurry of top-level diplomatic activity in the region.
Ban visited the Aida refugee camp in
Bethlehem [AFP]
Ban Ki-moon, the UN secretary general, visited the West Bank town of Bethelhem and later held talks with Abbas.
The UN chief said the time was not right to meet with Haniya and urged the Palestinian government to agree to the West's demands.
"I expect that with this formation of the national unity government, the leaders of this government will abide by the principles laid out by the Quartet," he said.
Rice warning
Despite the flurry of activity, a senior aide to Abbas warned the US that Palestinians needed to see results if the US was to make any headway in its efforts to resolve the conflict.
Nabil Abu Rudeina said he has told Rice that US efforts "will lead only to frustration" if Palestinians see no progress on the ground.
"If the American administration wants its peace efforts to succeed it must force Israel to enter into serious negotiations,"  Abu Rudeina told Palestinian television.
"The shuttle visits to discover horizons of the peace process without results on the ground will lead only to frustration in the Arab and Palestinian street," he added.