RAMALLAH, West Bank, July 12 (Reuters) - The Palestinian leadership, in unusually harsh criticism of Washington, on Tuesday held the United States responsible for "racist" Israeli policies it said had sabotaged the peace process.

The leadership said recent developments had confirmed the need for the Palestinians to go to the U.N. General Assembly in September to seek international recognition for a state of Palestine on lands occupied by Israel since 1967.

The Palestine Liberation Organisation's (PLO) executive committee convened in Ramallah after a meeting in Washington of the Quartet of Middle East peace mediators on Monday failed to announce any progress towards reviving peace talks.

The Quartet comprises the United States, Russia, the European Union and the United Nations.

The PLO said Israeli Prime Minister Benjamin Netanyahu's government aimed to prevent any resumption of negotiations and the establishment of an independent Palestinian state.

"The only option facing the world today, especially the United States, is to use all tools to oblige the occupiers to halt their racist, expansionary policy," the PLO said in a statement released after its meeting.

"The United States bears the prime responsibility for the continuation of this racist (Israeli) policy," it said.

President Mahmoud Abbas has said the Palestinians will seek international recognition for Palestinian statehood at the U.N. General Assembly if there is no resumption of peace talks by September.

The United States has said it will oppose any Palestinian attempt to secure full membership of the United Nations at the September meeting. It describes it as a unilateral step that will have no more than symbolic value.

Israeli officials worry it is part of a new Palestinian strategy aimed at isolating and "delegitimising" Israel.

U.S. President Barack Obama's efforts to revive the two-decade old Middle East peace process were derailed last year when face-to-face negotiations were halted by a dispute over Israeli settlement expansion in the West Bank.

The West Bank, together with the Gaza Strip and East Jerusalem, are territories occupied by Israel in the 1967 Middle East war and where the Palestinians aim to found an independent state alongside Israel.

Netanyahu said on Monday he was willing to sit down with Abbas "to open direct negotiations, but regrettably they refuse", according to a statement issued by his office. (Writing by Tom Perry, editing by Tim Pearce)