US President Barack Obama on Tuesday warned that he remained ready to use force over Syria's chemical weapons as he demanded that the United Nations take action.
In a somewhat defensive speech at the UN General Assembly, Obama said the United States was ready to defend interests in the Middle East, including ensuring "free flow of energy" and prohibiting weapons of mass destruction.
"The United States of America is prepared to use all elements of our power, including military force, to secure these core interests in the region," Obama told world leaders.
Obama said that the world's credibility was at stake after Syrian President Bashar Al-Assad's alleged use of chemical weapons.
"There must be a strong (UN) Security Council resolution to verify that the Assad regime is keeping its commitments, and there must be consequences if they fail to do so," Obama said.
"If we cannot agree even on this, then it will show that the UN is incapable of enforcing the most basic of international laws.
"On the other hand, if we succeed, it will send a powerful message that the use of chemical weapons has no place in the 21st century, and that this body means what it says," he said.
Obama lashed out at critics who questioned whether Assad carried out the August 21 chemical attack near Damascus, which US intelligence says killed some 1,400 people.
"These rockets were fired from a regime-controlled neighborhood and landed in opposition neighborhoods," Obama said.
"It is an insult to human reason -- and to the legitimacy of this institution -- to suggest that anyone other than the regime carried out this attack," he said.
Obama, who rose to power as a critic of the Iraq war, faced strong opposition from some of his base over his threats to use force in Syria.
But Obama argued that his willingness to use force has triggered action and cast the Syria debate with a wider lens.
"I do not believe that military action -- by those within Syria, or by external powers -- can achieve a lasting peace. Nor do I believe that America or any nation should determine who will lead Syria," Obama said.
"Nevertheless, a leader who slaughtered his citizens and gassed children to death cannot regain the legitimacy to lead a badly fractured country," he said of Assad.
"Should we really accept the notion that the world is powerless in the face of a Rwanda or Srebrenica?" said Obama, referring to two of the worst mass atrocities in the 1990s.
"If that's the world that people want to live in, then they should say so, and reckon with the cold logic of mass graves," he said.
Obama's remarks come as the United States and Russia wrangle over a UN Security Council resolution that would accompany an agreement by Syria to give up chemical weapons.
The US-Russia deal at least temporarily halted a push by Obama, supported by France, for a military strike on Syria.
In his speech, Obama announced that the United States would provide another $340 million in humanitarian aid for the Syrian crisis, which has produced some two million refugees.
The State Department said that the aid brings the US contribution to nearly $1.4 billion and includes support for food, clean water and shelter.