In an interview conducted through several of his lawyers with imprisoned Fatah leader Marwan Barghuti, an influential leader with widespread support among the Palestinian public, told AFP he was fully supportive of the bid to seek UN membership for a state on the lines that existed before the 1967 Six Day War.
He urged Palestinians and their supporters overseas to launch massive rallies in support of the move, which is due to take place when the United Nations General Assembly meets in September.
And he said it was "scandalous" that the rival Palestinian national movements Fatah and Hamas had not cemented their reconciliation agreement before the historic attempt to join the United Nations.
Any move by the United States to veto the request at the UN Security Council, which must approve all petitions for membership, would have grave consequences, Barghuti said.
"The US veto would be terrorism and aggression against the will of the international community -- particularly given that four-fifths of the world's population support a Palestinian state," he said.
"It would mark a turning point in US-Palestinian relations and put an end to the Palestinians relying on US sponsorship of the failed peace process, which both the United States and Israel are responsible for ruining."
As one of the five permanent members of the Security Council, Washington has made clear it will use the veto if the Palestinians ask the Security Council for membership this September, and Israel has also vehemently opposed the Palestinian bid.
But Barghuti said the United States "will lose, if it stands against the international community in defence of the occupation and the settlements and the discriminatory, racist system in Israel."
A lifelong activist who supported the Oslo peace process in the 1990s, Barghuti is widely believed to have masterminded the second intifada, or Palestinian uprising, that erupted in 2000.
A senior official within the Fatah movement, Barghuti was arrested in 2002 and two years later, sentenced to five life terms for murder for his role in several deadly anti-Israeli attacks.
He has since said he never supported attacks on civilians inside Israel and in recent years, has thrown his support behind peaceful resistance.
The UN bid was an opportunity for the Palestinians to "free themselves," he said, although he is under no illusion that gaining membership in the world body would end the Israeli occupation.
"Of course, the September step will not alone achieve our national rights, but it's a step in that direction and a chance for the Palestinian leadership to start a new approach... and make a radical change in dealing with Israel."
It will be "an important Palestinian and international step, a quantum leap and a first move in the direction of a new Palestinian strategy of action."
Such a step would allow the Palestinians to challenge "the US monopoly over the Palestinian issue and Israel's blackmail, and to turn instead to the international community to get Palestinian national rights," he said.
Barghuti, who has been mentioned as a potential successor to Palestinian president Mahmud Abbas, said the diplomatic plan was a non-partisan move and deserved backing from Palestinians at home and their supporters abroad.
"The Arab and Muslim world and everyone in the world who loves freedom and peace and justice should launch million-man marches when the UN vote happens," he said.
"The battle for UN membership for Palestine is not something to be fought by the president alone, it is for every citizen, every Palestinian, every Arab to fight on the ground.
"We strongly believe that political and diplomatic efforts don't achieve anything without resistance on the ground."
But Barghuti also warned that longtime political rivals Fatah and Hamas needed to make greater efforts to implement a reconciliation deal they signed in Cairo in May.
The two groups have committed to forming an interim government of independents to shepherd the population towards legislative and presidential elections by May 2012.
But three months after they signed the unity deal, no government has been formed, with talks stalled over whether Abbas's current prime minister Salam Fayyad will stay on, despite strong Hamas opposition.
"The continuing division is scandalous," Barghuti said.
"Before going to the UN, we need a Palestinian government, and it is unreasonable to cripple national unity by failing to form one.
"Unfortunately, some leaders do not realise that we are still at the stage of national liberation, and to move forward we need something very obvious: unity of the people, of the factions and of the social and political forces against the occupation."