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Jerusalem • Israel on Thursday abruptly called off a release of Palestinian prisoners, sending U.S. Secretary of State John Kerry's troubled Mideast peace efforts further into a tailspin.

The Israeli announcement, made in reaction to a renewed Palestinian push for membership in United Nations agencies, deepened the crisis in U.S.-led peace talks and made Kerry's goal of extending negotiations past a late-April dateline a more distant possibility.

Israel's chief negotiator, Tzipi Livni, said the Palestinians' decision to seek accession to 15 international conventions through the U.N. violated the terms of the promised prisoner release, which would have been the fourth since talks resumed last summer. The Palestinians submitted their applications after Israel failed to carry out the release, as promised, by the end of March. Israel carried out the first three prisoner releases, but balked at the final one without assurances that the Palestinians would extend negotiations.

"New conditions were established and Israel cannot release the fourth batch of prisoners," Livni said in a statement.

Earlier Thursday, a frustrated Kerry exhorted leaders on both sides to "lead" and to do so now to prevent the negotiations from collapsing.

Kerry called it a "critical moment" for the peace process and vowed to continue his efforts "no matter what." But he added there are limits to what the Obama administration can do to push the parties together and said it would be a "tragedy" if the talks failed.

"You can facilitate, you can push, you can nudge, but the parties themselves have to make fundamental decisions and compromises," he said. Israel and the Palestinians resumed peace talks last July, agreeing to a nine-month negotiating period with the aim of reaching a final peace deal. Kerry is now trying to broker a more modest "framework" agreement, in hopes of extending talks past the April 29 deadline through the end of the year to complete a deal.

Under the original negotiating formula, Israel promised to release 104 long-serving Palestinian prisoners in four groups, while the Palestinians put on hold their campaign for joining U.N. agencies. After the Palestinians won acceptance as a nonmember state at the U.N. General Assembly in 2012, they now qualify for membership in dozens of international agencies. Israel says that joining these bodies is an attempt to bypass negotiations. It also fears the Palestinians will use their newfound status to push an anti-Israel agenda.