UNITED NATIONS — Exhorting world leaders to push past years of cynicism and pessimism, President Barack Obama today challenged the countries of the United Nations to unite around peace efforts that he said could achieve agreement within a year to create an independent Palestine and a secure Israel.

Obama, in a speech to the U.N. General Assembly, urged fellow world leaders to press forward with renewed determination in the quest for Mideast peace, an effort that he acknowledged has encountered "few peaks and many valleys."

Without an agreement, he said, "more blood will be shed" and "this Holy Land will remain a symbol of our differences, instead of our common humanity."

Obama's one-year timeline is ambitious even if the Mideast peace process faced the best of circumstances, which it does not. He made no mention of the militant Hamas movement, which controls the Gaza Strip and refuses to accept Israel's right to exist.

Obama spoke with resolve of the need to address trouble spots around the world, but he tended first to the economic concerns that abound both at home and abroad.

"There is much to show for our efforts," he said, recalling the economic turmoil of years past. "We cannot — and will not — rest until these seeds of progress grow into a broader prosperity for all Americans and for people around the globe."