Palestinian president Mahmud Abbas warned Tuesday of legal and diplomatic action to stop Israeli settlement expansion, on the eve of a new peace mission by US Secretary of State John Kerry.
Abbas's warning came after Israel freed 26 prisoners earlier in the day, as part of US-brokered peace talks, which Kerry hopes to reinvigorate during his visit.
The release prompted celebration among Palestinians, who welcomed the prisoners back into the West Bank and Gaza Strip after they had spent two to three decades in Israeli jails.
But as Kerry geared up for his 10th visit since March, an anticipated announcement by Prime Minister Benjamin Netanyahu's government of further settlement construction looked set to cast a new cloud over the talks.
Abbas warned the Palestinians would take action to halt any such construction in territories they expect to form part of their promised state.
"We will not remain patient as the settlement cancer spreads, especially in (annexed Arab east) Jerusalem, and we will use our right as a UN observer state by taking political, diplomatic and legal action to stop it," he said.
"These actions show a lack of seriousness on the Israeli side in the negotiations and threaten to destroy the two-state solution."
Kerry has been pressing the two sides to agree on a framework for a final peace agreement ahead of an agreed late April target date for the talks to conclude.
The prisoners were the third batch of 104 detainees that Netanyahu pledged to release in four stages when the peace talks were revived in July. All were imprisoned before the 1993 Oslo accords, which launched the Middle East peace process.
Palestinians hailed the freed prisoners as heroes imprisoned for fighting against the Israeli occupation, with some welcomed back to Ramallah in the West Bank, others to east Jerusalem and the remainder into the Hamas-ruled Gaza Strip.
Gaza's Islamist Hamas rulers hailed the prisoner release, but reiterated their rejection of the peace talks and slammed the notion that freeing prisoners justified Israeli settlement expansion.
"The release of any prisoner is a gain for our people," Gaza's Hamas prime minister Ismail Haniya said.
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"But we reject negotiating with the occupation (Israel) and we do not accept that settlements should be expanded in exchange for that."
Netanyahu meanwhile criticised the hero's welcome given to the released prisoners, who had served 19 to 28 years after being convicted of killing Israeli civilians or soldiers.
"While we are prepared to take very painful steps in an effort to try and reach an agreement ... they, along with their highest leadership, are celebrating," he said.
"Murderers are not heroes."
A senior US State Department official speaking on condition of anonymity described the release as "really painful, difficult on the Israeli side".
Tuesday's release was expected to be accompanied by an announcement of new construction plans for Jewish settlements in the occupied West Bank, including east Jerusalem, as the previous two prisoner releases were.
Such a move is likely to infuriate the Palestinians and the international community, providing a further challenge for Kerry, whose intense shuttle diplomacy managed to revive the talks after a three-year hiatus.
But Netanyahu has come under strong pressure from hardliners both within his rightwing Likud party and its more hawkish coalition partners to take a stand.
Kerry will also have to quell tensions that rose after an Israeli ministerial committee on Sunday gave initial approval to a bill annexing Jordan Valley settlements, a largely symbolic move expected to be shot down by the government.
Abbas reiterated total rejection of Israel's demand to maintain a military presence in the Jordan Valley, where the West Bank borders Jordan.
"We have said that the Palestinian people is the one most in need of security, and is the one who needs guarantees of protection against the aggression of the occupation and the settlers."