Fears that the Syrian civil war and the Iranian nuclear standoff could provoke wider international conflict dominated the debate on Monday as world leaders gathered for the UN General Assembly.
The annual summit of the nations of the world was to begin on Tuesday, but the preliminary exchanges in New York quickly underlined the stark dangers facing the international community as several conflicts come to a head.
UN and Arab League peace envoy Lakhdar Brahimi told the UN Security Council that Syria is sinking deeper into bloodshed, with the regime complaining of an invasion of foreign fighters and the people facing growing food shortages.
And Iran's President Mahmoud Ahmadinejad stuck a typically defiant note, accusing Western powers of misusing UN veto powers to bully Tehran over its nuclear program and of standing by while critics of Islam commit "sacrilege."
Neither intervention augured well for consensus to emerge at the upcoming week of debate at the General Assembly, where leaders and senior officials from scores of powers great and small were to take the platform.
Brahimi's briefing underlined the scale and complexity of the Syrian crisis, with veto-wielding permanent Security Council members Russia and China still blocking Western efforts to build support for robust international action.
He told the 15-nation council the Syrian government estimates there are 5,000 foreign fighters in the country and is increasingly portraying the conflict as a "foreign conspiracy," envoys at the closed meeting told AFP.
Reporting on recent talks with Syria's President Bashar al-Assad, the former Algerian foreign minister painted a grim picture of life for those caught up in an 18-month-old conflict in which activists say more than 29,000 have died.
Brahimi told the council that the torture of detainees has become "routine" and that people were now afraid to go to hospitals which were in the hands of government forces for fear of facing abuse or detention.
The envoy estimated that 1.5 million people have now fled their homes and said Syria faces growing food shortages because harvests have been slashed by the fighting between government forces and opposition rebels.
There was also little sign of a breakthrough in the Iranian stand-off, in which the United States and its allies hope sanctions will force Tehran to scale back its nuclear ambitions and open them to international scrutiny.
Absent a climb-down by Tehran, Israel has warned it might launch pre-emptive strikes against Iranian targets, plunging the Middle East into a whole new round of uncertainty with global economic and political consequences.
But Ahmadinejad arrived for his annual show-down on enemy territory in New York in a belligerent mood, declaring that the United States, Britain and France "violate the basic rights and freedoms of other nations."
He said that it was wrong for the five major powers to have a veto on the Security Council, which was why the body "has failed to establish justice and ensure sustainable peace and security in the world."
And he sought to link his charge of illegitimacy to the West's failure to prevent filmmakers and cartoonists from, in his view, committing "sacrilege against people's beliefs and sanctities."
There has been widespread outrage in the Muslim world this month following the release of a movie trailer made by a Christian extremist group in California and new French cartoons lampooning the Prophet Mohammed.
The Arab Spring revolutions in Tunisia, Libya and Egypt have brought a new generation of Islamist leaders to power and the conflict between Western respect for free speech and Muslim opposition to blasphemy has strained ties.
This week's General Assembly will be the first attended by Egypt's President Mohamed Morsi, a former leader of the Islamist Muslim Brotherhood who is now leader of the biggest country in the Arab world.