US officials confirmed that the top American diplomat had begun surprise talks with Livni, as they took advantage of both being in London at the same time for different meetings.
Their talks came after Kerry met in the British capital with Palestinian leader Mahmud Abbas in the wake of the collapse last month of the peace process.
"Secretary Kerry will have an informal meeting with Israeli Justice Minister Livni this afternoon," a senior State Department official said earlier.
Kerry, who was in London for talks on Syria had stressed to Abbas yesterday that the fate of the talks lies in the hands of the Israelis and Palestinians.
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Kerry "reiterated the need for any Palestinian government to recognise Israel, commit to non-violence, and abide by previous agreements," a US official said in a statement.
He also "urged both sides to refrain from unhelpful steps".
Kerry coaxed the Israelis and the Palestinians back to the negotiating table in July 2013 after a three-year hiatus, and both sides agreed to keep talking for nine months.
Israeli Prime Minister Benjamin Netanyahu today accused the Palestinians of teaching their children that Israel "should be made to disappear".
The Israeli answer was to "continue building our country and our unified capital, Jerusalem", said the rightwing premier.
In more violence in the region, Israeli border police shot dead two Palestinians today during a demonstration in the West Bank marking the 66th anniversary of the Nakba, or "catastrophe" of the Jewish state's creation in 1948.