The overnight raids targeted Islamic State (IS) group fighters whose fierce assault in the area prompted more than 130,000 civilians to flee across the border into Turkey.
They followed the first strikes by Washington and its Arab allies on Tuesday against IS in other parts of Syria in which at least 120 IS and Al-Qaeda militants were said to have been killed.
Washington said those raids had partly targeted extremists plotting an "imminent attack" against the West.
US President Barack Obama, who hailed the strikes as a sign the world is united in confronting the jihadists, will be among the first leaders to address the General Assembly in New York.
He then chairs a special UN Security Council meeting due to adopt a resolution on stemming the flow of foreign fighters to Iraq and Syria, only the second time the US president leads a session of the top world body.
About 12,000 foreign fighters have travelled to Syria and Iraq from 74 countries, in the biggest such mobilisation since the Afghan war of the 1980s, according to the London-based International Centre for the Study of Radicalisation.
The overwhelming majority of foreign fighters -- up to 75 percent -- are from the Middle East and Arab countries, with Saudi Arabia, Tunisia and Morocco topping the list.
Branded a terrorist organisation by the United States and the United Nations, IS controls large swaths of territory in Iraq and Syria, and has beheaded two US journalists and a British aid worker.
The Syrian Observatory for Human Rights said at least 50 Al-Qaeda militants were killed, as well as more than 70 IS members. Eight civilians, including three children, were also among the dead.
Syrian state media said the latest coalition raids struck near the Kurdish town of Ain al-Arab, or Kobane, which the Islamic State group has been battling to capture for a week.
