A US deadline for reaching a Middle East peace deal between Israel and the Palestinians has passed without agreement.
The latest round of talks was halted last week after the two main Palestinian factions, Fatah and Hamas, agreed to form a unity government.
Israeli Prime Minister Benjamin Netanyahu said the agreement was a "giant leap backward" for the peace process.
Meanwhile, US Secretary of State John Kerry has denied he had ever called Israel "an apartheid state".
The controversy came over comments he reportedly made during a private meeting.
"Israel is a vibrant democracy and I do not believe, nor have I ever stated, publicly or privately, that Israel is an apartheid state or that it intends to become one," Mr Kerry said.
His statement came after calls for him to resign or at least apologise for the alleged comments.
"Anyone who knows anything about me knows that without a shred of doubt," he said.
But Mr Kerry, who has seen his efforts to broker peace between Israel and the Palestinians collapse, did suggest that he had used a poor choice of words during his speech on Friday to international experts of the Trilateral Commission.
He said: "I have been around long enough to also know the power of words to create a misimpression, even when unintentional, and if I could rewind the tape, I would have chosen a different word to describe my firm belief that the only way in the long term to have a Jewish state and two nations and two peoples living side by side in peace and security is through a two-state solution."
The Daily Beast online news site reported that Mr Kerry had warned that "a unitary state winds up either being an apartheid state with second-class citizens - or it ends up being a state that destroys the capacity of Israel to be a Jewish state".
The website said it had been given a recording of Mr Kerry's speech, which sparked a furore in Israel and led one Republican senator in the US to call for his resignation.
Senator Ted Cruz said Mr Kerry had "repeatedly demonstrated a willingness to countenance a world in which Israel is made a pariah".
He said Mr Kerry should offer his resignation "before any more harm is done to our national security interests and our critical alliance with the state of Israel".
In his statement, Mr Kerry said: "I will not allow my commitment to Israel to be questioned by anyone, particularly for partisan, political purposes."
Tonight, Mr Kerry said he had no regrets about the energy he poured into his failed peace bid and would dive back in again if asked.
His spokeswoman Jen Paski said Mr Kerry, who single-handedly dragged Israel and the Palestinians back to the negotiations after a three-year hiatus, has "no regrets about the time he spent investing in this process."
"We've reached a point... where a pause is necessary... a holding period, where parties will figure out what they want to do next," she said.