In an emotional appeal to world leaders meeting in New York, Lebanon's prime minister on Friday said his country is facing a "fierce terrorist onslaught" and a national disaster created by more than a million Syrian refugees flooding the tiny nation.

Speaking before the U.N. General Assembly, Tammam Salam said Lebanon is determined not to give in to "pressure and blackmail" by Islamic extremists who overran a town bordering Syria in August and are holding about 20 Lebanese soldiers and policemen hostage.

The Islamic State, an al-Qaida breakaway group, has already beheaded two of them and the Nusra Front, the main al-Qaida branch in Syria, has shot a third, sparking days of violence against Syrian refugees in Lebanon.

Since then, Lebanese troops have clashed with jihadist fighters in the border area near the Lebanese town of Arsal.

The extremists have made various demands in exchange for the soldiers' release, including the release of Islamist prisoners in Lebanese jails.

"We will never give in to such pressure, and will remain focused on the release of our soldiers, while preserving our country," Salam said.

Lebanon has long been split over the war in neighboring Syria, with Sunnis supporting the Sunni-led rebellion against President Bashar Assad and Shiites supporting his government, fearing the rise of extremists among the rebels' ranks. The Shiite Hezbollah movement has infuriated many Sunnis by sending fighters to battle alongside Assad's troops.

Salam also said the number of Syrian refugees flooding tiny Lebanon — a number equivalent to one-third of the Lebanese population — is now a national disaster.

"To be fully aware of the implications of this situation, one should imagine a hundred million people — yes, one hundred million people — flocking massively into the United States and spreading randomly in cities, towns, schools and parks," he said.

Salam met with U.S. Secretary of State John Kerry early Friday.

A senior State Department official said Kerry underscored the United States' firm commitment to Lebanon's security and stability at a time when Lebanon is facing many challenges.

Kerry also commanded Salam for Lebanon's efforts to combat the Islamic State group within its borders and praised Lebanon's support for efforts to counter the extremists.

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AP Diplomatic Writer Mathew Lee contributed to this report from New York.