Hardline nationalist Lieberman was a controversial foreign ministry choice
Israel's new ultra-nationalist foreign minister has said it is not bound by a US-sponsored 2007 agreement to reach a peace deal with the Palestinians.
"The Annapolis conference, it has no validity," Avigdor Lieberman said.
He was speaking at a handover ceremony at the foreign ministry, prompting his predecessor Tzipi Livni to interrupt and diplomats to shift uncomfortably.
At Annapolis, each side agreed to further discussions aimed at creating an independent Palestinian state.
Palestinian officials described Mr Lieberman as an "obstacle to peace" whose policies would rebound negatively on Israel.
"Nothing obliges us to deal with a racist person hostile to peace such as Israeli Foreign Affairs Minister Lieberman," Yasser Abed Rabbo said in comments to AFP news agency.
Correspondents say officials at the foreign ministry seemed taken aback at such a sudden and public repudiation of one of the main planks of Israeli diplomatic activity.
"There is one document that obligates us - and that's not the Annapolis conference, it has no validity," Mr Lieberman said.
The document he was referring to was the international peace plan known as the Road Map, signed in 2003, while "the Israeli government never ratified Annapolis, nor did parliament".
The Annapolis accords were seen as a last-ditch attempt by the previous US administration to realise what President George W Bush called his "vision" of peace involving a two-state solution.
The Israeli and Palestinian leaders agreed to launch "vigorous, ongoing and continuous" negotiations to reach a comprehensive peace deal, and make every effort to conclude it before the end of 2008.
Although the incoming Netanyahu government has avoided committing itself to the establishment of a Palestinian state, the Road Map endorsed by Mr Lieberman was also meant to achieve that aim.
Middle East envoy Tony Blair earlier warned Israel that the Palestinians must have their own state to avoid a major conflagration in the region.
"The alternative to a two-state solution is a one-state solution. If there is a one-state solution there is going to be a big fight," the former UK prime minister said on a visit to Brussels.
After Mr Lieberman's comments were published, a spokesman for the White House National Security Council, Mike Hammer, said the Obama administration remained "committed to the establishment of a democratic Palestinian state living side by side with Israel in peace and security".
Mr Hammer said that the administration was expecting "frank discussions", but that it was looking forward to "working vigorously with the new Israeli government".
He stressed that any discussions would be based on an underlying shared commitment to Israel and its security.
Mr Lieberman, known for his outspoken criticism of Arab citizens of Israel and some Arab leaders, was a controversial choice for foreign minister in the government of right-winger Benjamin Netanyahu which was sworn in on Tuesday.
In his speech, he admitted voting against Israel's ratification of the Road Map "but that is the only document that obligates us, it is the only document that was ratified by the government and the Security Council, and it binds this government as well".
Asked about the new foreign minister's comments, political sources close to Mr Netanyahu were quoted saying they largely reflected the new leader's position.
The Road Map made progress towards a Palestinian state contingent on the Palestinian Authority's progress on suppressing activity by militant groups - the strongest of which, Hamas, actually ousted the Fatah-dominated Palestinian Authority from Gaza in 2007.
It also obliges Israel to freeze settlement activity on territory it occupied in the 1967 war.
Mr Netanyahu's cabinet is the largest in Israel's political history combining centre-right, centre-left and far-right parties.
Ms Livni's Kadima party, which backs a two-state solution, won the most seats in February elections, but was considered less likely to be able to form a coalition than a Likud-led right-leaning coalition.
Talks aimed at bringing Kadima into a unity government failed, with Ms Livni saying the parties' platforms were too different.