His remarks, at a news conference with visiting Italian Prime Minister Enrico Letta, came in the wake of Kerry's latest attempt to coax Israel and the Palestinians back into direct peace talks, in a visit which the chief Palestinian negotiator said had failed to achieve any breakthrough.
"Kerry made useful and constructive proposals and we are not saying they were bad, but they need further clarification and explanation before we can return to negotiations," Abbas said.
Although Kerry flew out of the region on Sunday, he left behind several of his advisers and is expected to return to the region soon, Abbas said.
Amin Maqbul, a senior official in Abbas's ruling Fatah movement, said there had been "progress" during Kerry's marathon talks and expressed appreciation for his commitment to the establishment of a Palestinian state along the lines that existed before the Six Day War of 1967.
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"Settlements remain the main obstacle to a resumption of negotiations," he said, calling for added US pressure on the Israeli government on all issues.
According to a Palestinian official, Kerry's proposal was based on a speech by US President Barack Obama in 2011 calling for a Palestinian state on the lines predating the Israeli occupation from 1967.
"The Palestinians told Kerry the initiative needed clarifications, particularly on the issue of cessation of settlement" which had not been addressed, the official told AFP on condition of anonymity.
"It is not clear whether the US will be permanently present in the negotiations or just intervene when necessary," he added.