United Nations: The Palestinians accused Israel on Monday of systematically destroying prospects for a two-state solution to their decades-long conflict with its continuing campaign of colony building.

Palestinian UN observer Riyad Mansour sent a protest letter to the UN secretary-general, Security Council and General Assembly two days before the Quartet of Mideast mediators — the US, UN, European Union and Russia — meets in Washington to discuss the long-stalled peace process.

Mansour said Israel's "illegal and destructive plans" to build new colonies underscore "the dubious nature" of its claims of readiness to negotiate a peace deal.

Israeli-Palestinian talks remain frozen over Palestinian demands that Israel stop building on lands they claim, and agree to negotiate borders based on lines Israel held before capturing the West Bank, Gaza and occupied east Jerusalem in 1967.

Israel rejects those conditions and has defied international pressure to freeze settlement construction. Israeli Prime Minister Benjamin Netanyahu insists that negotiations resume without what he has portrayed as preconditions.

"The main obstacle to peace is not colonies," Karean Peretz, spokeswoman for Israel's UN Mission, said on Monday. "It is the so-called ‘claim of return' and the Palestinian leadership's refusal to return to the negotiating table. We need direct negotiations, not more provocations at the UN."

The Palestinians have long demanded that Palestinian refugees and their descendants, who now number in the millions, be allowed to return to Israel. The Israeli government insists that the country must be recognised as the Jewish homeland, which would require the Palestinians to accept that most refugees will be denied the "right of return" to what is now Israel.

The Quartet has called for a resumption of Israeli-Palestinian negotiations with the goal of a peace agreement by the end of 2012. But in late February, UN political chief B. Lynn Pascoe told the Security Council that exploratory low-level talks in Amman, Jordan between the Israelis and Palestinians had stalled and prospects for resuming direct negotiations "remain dim."

Nonetheless, the Quartet on March 12 again urged the Israelis and Palestinians to return to negotiations and reach an agreement no later than the end of the year.