The Palestinian leadership is under mounting pressure to abandon or modify its bid to win full UN membership, as a top Israeli diplomat admitted his country's battle to prevent recognition of a Palestinian state was lost and warned of "violence and bloodshed" ahead.

Mohammad Shtayyeh, a senior member of the Palestinian team heading for New York next week, said: "There is very, very serious pressure on us but at the end of the day Abu Mazen [Palestinian president Mahmoud Abbas] ... has no choice‚ and no one can blame him." Twenty years of negotiations had got nowhere, he said.

Amid intensifying diplomatic efforts to avoid a potentially damaging collision with the US, a series of high-level diplomatic delegations has visited Abbas over the past week. The US secretary of state, Hillary Clinton, telephoned the Palestinian president to appeal to him to "avoid a negative scenario" when the UN general assembly opens in less than two weeks.

President Obama's Middle East envoy David Hale and senior adviser Dennis Ross travelled to Ramallah on Thursday, the day after the Quartet on the Middle East envoy, Tony Blair, visited Abbas. The two delegations urged a return to peace negotiations with Israel instead of the UN strategy.

"The intention is to block us from going to the UN," said Shtayyer. But, he added, there is "nothing in writing in front of us from the Quartet or the US".

He insisted the Palestinians would not be diverted unless they were guaranteed talks on the basis of the pre-1967 borders, a total settlement freeze and the dropping of Israel's insistence that it is accepted as a Jewish state.

"The decision on our side is very clear. We are asking for full membership," he said. He said the bid was "the beginning of the game not the end" and UN recognition did not preclude a return to negotiations. "We see no contradictions between doing both," he said.

Israel's ambassador to the UN, Ron Prosor, said his country was "in a battle to stem the tide". He told the Israeli newspaper Ma'ariv: "This is a diplomatic endeavour against all odds. I am trying, literally down to the last moment, to persuade the ambassadors of UN member countries that this unilateral course of action by the Palestinians won't lead to peace and won't lead to the establishment of a Palestinian state, but only to violence and bloodshed."

He said it was "clear to me that we can't win the vote" because the Palestinians had an automatic majority in the general assembly. Israel was instead trying to enlarge its "moral minority" at the world body, he said.

The Palestinians are thought to have the support of up to 140 countries at the general assembly, exceeding the two-thirds majority needed for a resolution to pass. However, admission to the UN as a member state requires the approval of the security council, which the US has made clear it will veto.

The Obama administration is anxious to avoid using its veto, fearing such a move will alienate Arab states with whom its relations are already fragile following the unrest sweeping the Middle East this year. However Obama is also keen to prove his pro-Israel credentials in the run-up to next year's presidential elections.

The UN general assembly opens on 21 September with an address by Obama. Abbas is expected to deliver his speech two days later in which, Shtayyer said, "he will urge the security council not to [use its] veto". However, they would seek a vote at the general assembly "the moment we get the US veto".

The Palestinian people were "in full support of this strategy", he added. However a recent poll by the Palestinian Centre for Public Opinion in the West Bank and Gaza found that almost 60% of respondents preferred to resume negotiations with Israel before going to the UN.

Israeli security forces are preparing for widespread violent protests by Palestinians around the time the general assembly meets, although Abbas has urged that demonstrations be peaceful. Both sides acknowledge that clashes could be triggered by attacks by rightwing settlers. On Thursday, olive trees were uprooted, cars set ablaze and a mosque vandalised near Nablus, according to Palestinian officials.