* Crisis focused on delayed release of jailed Palestinians
* Kerry cancels planned face-to-face talks with Abbas
* Peace talks facing April 29 deadline
* Israel's Lieberman says Israel did all it could and next move up to Palestinians (Adds first Israeli comment on talks crisis, Foreign Minister Lieberman)
By Noah Browning
RAMALLAH, West Bank, April 2 (Reuters) - Washington said on Wednesday it was endeavoring to put Israel-Palestinian peace negotiations back on track despite recent "unhelpful, unilateral actions" by both sides.
A surprise decision by Palestinian President Mahmoud Abbas on Tuesday to sign more than a dozen international conventions that could give Palestinians greater leverage against Israel left the United States searching for a way to keep the talks going past an April 29 deadline.
"We are disappointed by the unhelpful, unilateral actions that both parties have taken in recent days," White House spokesman Josh Earnest told reporters aboard Air Force One as President Barack Obama headed to Michigan.
He said Secretary of State John Kerry was "in close touch with our negotiating team, which remains on the ground in the region to continue discussions with the parties".
Israeli and Palestinian negotiators were due to meet later in the day with U.S. envoy Martin Indyk, according to sources familiar with the talks.
In its first comment on the crisis, Israel said it was up to Abbas to resolve the standoff.
Israeli Foreign Minister Avigdor Lieberman said Israel had done "all it could to try and reach a settlement with the Palestinians, and now the ball is in their court."
The Palestinians had handed over to a U.N. representative and other diplomats applications to join 15 international conventions. They include the Geneva Conventions, the key text of international law on the conduct of war and occupation.
A senior Palestinian official, voicing frustration exacerbated by Israel's failure to carry out a pledged release of several dozen Palestinian prisoners, said on Wednesday that the eight-month-old talks had become merely "negotiating about negotiating".
Palestinian officials said Israel's failure to free the prisoners meant Abbas was no longer bound to a commitment not to confront it at the United Nations and other international bodies.
The developments further complicated efforts by Kerry to piece together a three-way deal to push the faltering negotiations into 2015.
The talks were already in trouble over the issues of Israeli settlements in the West Bank and East Jerusalem, land captured by Israel in the 1967 Middle East War, and Palestinian opposition to Netanyahu's demand to recognise Israel as a Jewish state.
Israel had said it first wanted a Palestinian commitment to negotiate past the original target date for a deal before freeing the last of the 104 prisoners it promised to release as part of U.S. efforts to restart the negotiations last July.
"UP TO THE PARTIES"
Kerry had cancelled a planned visit to the West Bank city of Ramallah on Wednesday to meet Abbas, saying it was important to keep the peace process moving but "in the end, it is up to the parties".
Palestinians hope Abbas's move will give them a stronger basis to appeal to the International Criminal Court and eventually lodge formal complaints against Israel for its continued occupation of territory seized in 1967, lands they see as vital to an independent state. Most countries deem the Israeli settlements illegal.
Yasser Abed Rabbo, deputy head of the PLO, cautioned on Wednesday against simply returning to an "empty routine" at the negotiating table. He reaffirmed that Palestinians wanted talks to focus on setting the future borders of their state.
"We can't return to the empty routine, a search for a framework for talks - this empty routine which is negotiating about negotiating," he told reporters.
Continuing the talks beyond the end of this month, he said, "must proceed from and depend on one main point, and this is looking into the issue of borders."
The conventions signed by Abbas were mostly sets of international standards on social and rights issues, such as conventions against discrimination against women and for the rights of disabled people as well as the Geneva Conventions.
Law professor Robbie Sabel, a former legal adviser to the Israeli Foreign Ministry, described Abbas's signature on the conventions as "merely symbolic". He noted Abbas had stopped short of applying for membership in international organisations.
Kerry made an unscheduled visit to Jerusalem on Monday seeking to extend the negotiations by putting together a proposal that included the possible release of Jonathan Pollard, an Israeli spy jailed in the United States in the 1980s.
The package, officials close to the talks said, included an additional Israeli release of hundreds of jailed Palestinians and a possible partial freeze on the settlements.
Pollard, a U.S. citizen and former navy analyst, is serving a life term for spying for Israel. His freedom would be a political triumph for Netanyahu, making it easier for him to sell a wider release of jailed Palestinians to cabinet members and a sceptical Israeli public. (Additional reporting by Ali Sawafta in Ramallah, Lesley Wroughton in Brussels, Jeff Mason aboard Air Force One and Maayan Lubell and Allyn Fisher-Ilan in Jerusalem, Editing by Jeffrey Heller, Angus MacSwan, Toni Reinhold)