US President-elect Donald Trump speaks during a USA Thank You Tour event at Giant Center in Hershey, Pennsylvania, December 15, 2016. Lucas Jackson/Reuters President-elect Donald Trump addressed the humanitarian crisis unfolding in Syria's largest city during a rally Thursday night, calling it "sad" and promising to set up "safe zones" so that "people will have a chance."

“When I look at what’s going on in Syria, it’s so sad,” he told a crowd in Pennsylvania. “It’s so sad, and we’re going to help people.”

Trump said the money for the safe zones — complicated and expensive projects that require a substantial commitment of military resources, including ground troops — would come from the Gulf states.

"They have nothing but money," he said, likely referring to some combination of Saudi Arabia, Qatar, and the United Arab Emirates, which have supported the Syrian revolution throughout the course of the five-plus-year civil war.

"We don't have money," Trump said. "We owe $20 trillion. I will get the Gulf states to give us lots of money, and we'll build and help build safe zones in Syria, so people can have a chance. So they can have a chance."

Thursday night was not the first time Trump has proposed setting up safe zones inside Syria that would be paid for by the Gulf states.

Trump — who has said that he opposes arming Syrian rebels trying to overthrow Syrian President Bashar Assad because "we don't even know who they are" — has presented the safe zones as an alternative to accepting Syrian refugees into the US.

This frame grab from Tuesday, December 13, 2016, video shows people walking among damaged buildings on a street filled with debris near the ancient Umayyad Mosque, in the Old City of Aleppo, Syria. AP Photo

"What they should do is, the countries should all get together, including the Gulf states, who have nothing but money, they should all get together and they should take a big swath of land in Syria and they do a safe zone for people, where they could go to live, and then ultimately go back to their country, go back to where they came from," he told CBS' "Face the Nation" in October 2015.

Trump repeated the idea one month later, during a rally in Knoxville, Tennessee.

“What I'd like is to build a safe zone in Syria," he said. "Build a big, beautiful safe zone, and you have whatever it is so people can live, and they’ll be happier ... So you keep them in Syria."

Russian President Vladimir Putin, right, shakes hands with Syrian President Bashar Assad during a meeting at the Kremlin in Moscow, October 20, 2015. Kremlin/Reuters

Building safe zones could complicate Trump's other policy position on Syria, however, which is to work with Assad and Russia to defeat the Islamic State. Assad and his allies, Russia and Iran, would likely see the construction of safe zones by the US and its partners as a violation of Syria's territorial sovereignty.

During the second presidential debate in October, Trump would not answer ABC News correspondent Martha Raddatz when she asked him what he would do, as president, about Syria and the humanitarian crisis in Aleppo, saying only that "I think Aleppo is a disaster, humanitarian-wise. ... I think that it, basically, has fallen."

Aleppo fell to pro-government forces earlier this week, after a month of intense bombing accompanied by a ferocious ground offensive killed nearly 1,000 rebel fighters and civilians in the eastern half of the city.

The opposition reached a deal with Russia on Wednesday for a cease-fire and the evacuation of approximately 40,000 civilians and opposition forces from the city. The evacuations were suspended on Friday, however, amid demands by Iran-backed, pro-government militias to first evacuate wounded civilians from Shi'ite villages around Aleppo that are being besieged by rebel fighters.