US President Barack Obama told world leaders on Wednesday to stop blaming America and join him in confronting challenges including the war in Afghanistan and nuclear programs in Iran and North Korea.
Russia signaled it might be ready to take a tougher stance on Iran, while Iranian President Mahmoud Ahmadinejad was expected to defend Tehran's nuclear ambitions in his own UN speech.
But as he readied his address, hundreds of Iranians protested outside the country's UN mission, highlighting tensions over his re-election in June polls the opposition charges were rigged.
Obama, in his first speech to the assembly since taking office in January, pledged US global engagement but said the United States could not shoulder the responsibility alone.
"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.
The US leader, enjoying a global spotlight, urged international leaders to move beyond "an almost reflexive anti-Americanism, which too often has served as an excuse for collective inaction."
Obama, who will host a Group of 20 nations summit in Pittsburgh this week, also pledged to work with allies to strengthen financial regulation to "put an end to the greed, excess and abuse that led us into disaster." [ID:nLH78576]
Obama was among the first major speakers at the gathering, which brings more than 100 heads of state and government together to air issues ranging from nuclear proliferation and international terrorism to climate change and global poverty.
Libya's Muammar Gaddafi, delivering his own inaugural UN address, took a swipe at the veto power wielded by the five permanent members of the UN Security Council. He called the group the "terror council" and demanded it be scrapped.
Obama has brought a new tone in US foreign policy, stressing cooperation and consultation over the unilateralism of his predecessor, George W Bush.
Despite Obama's global popularity, the new approach has delivered few concrete foreign policy achievements.
But both Russian and US officials signaled the two sides may be moving closer on a key issue: how to deal with Iran's nuclear program.
"It wasn't that long ago where we had very divergent definitions of the threat and definitions of our strategic objectives vis-a-vis Iran. That seems to me to be a lot closer, if not almost together," Michael McFaul, a White House adviser on Russia, said in New York.
All eyes were on Iran's Ahmadinejad, whose speech later on Wednesday could well be a sharp counterpoint to Obama's address.
Ahmadinejad recently drew fresh international condemnation for calling the Holocaust of 6 million Jews by Nazi Germany a lie and repeating Tehran's vow never to bargain away its nuclear program.
French President Nicolas Sarkozy had a warning for Iran in his speech to the Assembly.
"If they are relying on the passive response of the international community in order to pursue their military nuclear program, they are making a tragic mistake," he said
Russian President Dmitry Medvedev used his speech to again praise Obama's recent decision to scale back Bush-era plans for a European missile defense system that had worried Moscow.
After talks with Obama centered on the Iran issue, Medvedev indicated Russia might back moves to impose sanctions on Tehran if it continues to resist on the nuclear issue.
"Russia's position is simple: sanctions are seldom productive but they are sometimes inevitable," he said.
Brazilian President Luiz Inacio Lula da Silva, expected to be a key player at the G-20 Pittsburgh meeting, summed up the position of many developing countries in saying it was time to rethink the global economic balance of power.
Gaddafi -- expected to be one of the day's most colorful speakers -- ended up being one of the dullest.
The Libyan strongman's first New York speech came amid raw US emotions over the Lockerbie bombing after Scotland's release of a Libyan official convicted in the 1988 attack.
But the rambling 1-1/2 hour address, which touched on everything from the UN charter to the 1963 assassination of former US President John F. Kennedy, ended up driving some delegates from the room in boredom.