Mr Lieberman took over at the foreign ministry with a big political splash
Israel's former chief peace negotiator says the way the new government is talking shows it will not be a partner for peace with the Palestinians.
Tzipi Livni's criticism follows the rejection by her successor as foreign minister, Avigdor Lieberman, of recent US-backed efforts towards a peace deal.
"What happened is that the government announced that Israel is not relevant, is not a partner," she said.
New PM Benjamin Netanyahu has pledged to seek peace but has not detailed how.
Ms Livni's centrist Kadima party came narrowly ahead of Mr Netanyahu's right-wing Likud in the February election, but he was asked to form a coalition as right-leaning parties predominated.
In his speech on Wednesday, at a foreign ministry handover attended by Ms Livni, the ultra-nationalist Mr Lieberman said Israel was not bound by the Annapolis accords agreed with the Palestinians and the Bush administration in November 2007.
He said the only legitimate document was another US-sponsored deal, the Road Map peace plan of 2003, because he said it was ratified by the Israeli government and the UN Security Council.
In an interview with Israeli army radio, Ms Livni said hardliners had avoided peace efforts in the past with the "pathetic excuse" that there had been no partner on the Palestinian side.
Likud: 27 seats, 15 ministers
Yisrael Beiteinu 15 : 5 ministers
Labour: 13 seats, 5 ministers
Shas: 11 seats, 4 ministers
Jewish Home: 3 seats, 1 minister
United Torah Judaism: 5 seats
"From today, Israel has announced that it is not a partner," she said.
"The remarks do not represent Israel, the remarks hurt Israel," she added, and urged Mr Netanyahu to disavow them.
Correspondents say Mr Netanyahu has softened his opposition towards the Palestinians since his last premiership in the 1990s.
However, they add, the appointment of Mr Lieberman has angered Palestinians and raised international concerns because of his hard-line positions on the peace process and his manifesto which was widely seen as racist against Arabs.
Palestinian negotiator Saeb Erekat said Mr Lieberman's remarks were the first test for US President Barack Obama in the Middle East.
"He has slammed the door in the face of the US and the international community," he said.
No land for peace
US state department spokesman Gordon Duguid would not be drawn into commenting on Mr Lieberman's views when he briefed reporters in Washington.
Instead, he stressed Mr Netanyahu's stated commitment to achieving peace and said the administration would work closely to advance that cause.
Analysts say the Road Map never got off the ground because both sides accused each other of failing to meet their obligations.
Israel said the Palestinian Authority had not clamped down on militants, while Palestinians said Israel ignored a freeze on settlement activity on occupied territory.
Annapolis was designed to get over that hump by jumping directly to final status talks on Palestinian independence.
However, Annapolis too got stuck and had made little apparent progress by its initial deadline of the end of 2008.
After his speech, Mr Lieberman went further in a TV interview, saying he also opposed withdrawal from the occupied Golan Heights as part of peace negotiations with Syria.
He said he was "very much in favour of peace with Syria - but only on one basis - peace in return for peace" and not, by implication, a land-for-peace deal.
Syria says the Golan Heights, occupied by Israel in 1967, must be returned in full if there is to be peace between the two countries.