Palestinian president Mahmud Abbas said on Tuesday that US Secretary of State John Kerry had made "useful and constructive proposals" during his four-day visit last week, adding he was "optimistic" about the outcome.

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.

"We are optimistic because Kerry is serious and determined to reach a solution. We hope to go back to negotiations very soon in order to address the core issues between us and the Israelis," he added.

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.

"He has made it clear that this is US policy," he told Voice of Palestine radio, adding that there had also been progress on the issue of Israel's release of Palestinian prisoners.

"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.

"The Palestinians want east Jerusalem as the actual capital of their state, however there is no clear mention of this the initiative, even if it is part of the 1967 territories," another Palestinian 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.

But the optimism displayed by Abbas was not reflected on the ground, with a new Israel-Palestinian survey showing most people held little hope the talks would result in a resumption of direct talks after a hiatus of nearly three years.

According to a poll jointly conducted by the Harry S. Truman Research Institute for the Advancement of Peace at Jerusalem's Hebrew University and the Palestinian Centre for Policy and Survey Research in Ramallah, just over a quarter of Palestinians -- 27 percent -- and only one in 10 Israelis, believe that talks will resume and violence will end.

Just over two thirds of both peoples -- 68 percent of Israelis and 69 percent of Palestinians -- view the likelihood of a Palestinian state emerging in the next five years as low or non-existent.

And on both sides there is a high degree of suspicion of the other side's long-term intentions.

The poll found that 57 percent of Palestinians believe Israel wants "to extend its borders to cover all the area between the Jordan River and the Mediterranean Sea and expel its Arab citizens."

In Israel, 37 percent believe the Palestinians are, in the long term, planning "to conquer the State of Israel and destroy much of the Jewish population."

Some 62 percent of Israelis support a two-state solution while 33 percent oppose it, while among Palestinians, 53 percent are in favour and 46 oppose it.

But 58 percent of Palestinians believe a two-state solution is no longer viable.

The pollsters questioned 601 Israelis, giving a 4.5 percent margin of error, and 1,270 Palestinians, giving a 3 percent margin of error.