WASHINGTON (AP) — Struggling to break decades of hostility, President Barack Obama convened a new round of ambitious Mideast peace talks Wednesday and told Israeli and Palestinian leaders they faced a fleeting chance to settle deep differences.

“This moment of opportunity may not soon come again,” Obama said at the White House before hosting Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas in the first face-to-face peace talks in nearly two years. “They cannot afford to let it slip away.”

Obama sought to temper expectations, noting that it had taken his administration this long just to get the two sides back to the bargaining table.

“The hard work is only beginning,” Obama said. “Neither success nor failure is inevitable. But this much we know: If we do not make the attempt, then failure is guaranteed. If both sides do not commit to these talks in earnest, then long-standing conflict will only continue to fester and consume another generation, and this we simply cannot allow.”