"Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone," Obama said in a passage of the speech he was delivering Wednesday to the United Nations General Assembly.
The White House released excerpts in advance that carried a remarkably blunt tone.
It comes in Obama's first speech to this world body, a forum like none other for a leader hoping to wash away any lasting images of U.S. unilateralism under George W. Bush.
In essence, Obama's message is that he expects plenty in return for reaching out.
"We have sought in word and deed a new era of engagement with the world," Obama said, echoing the cooperative theme he promised as a candidate and has since used as a pillar of his foreign policy. "Now is the time for all of us to take our share of responsibility."