Republican presidential hopeful Donald Trump said Wednesday that Syrian refugees in the U.S. could be part of the Islamic State group and that he will send them home if he is elected president. While addressing a rally in Keene, New Hampshire, the real estate mogul also asked why Syrians fled their country instead of staying back and fighting the militants.

"I'm putting the people on notice that are coming here from Syria as part of this mass migration," Trump said, according to the Associated Press (AP). "If I win, they're going back," he said, later adding, "They could be ISIS, I don't know."

In his hour-long speech, the 69-year-old said the migration could be the refugees’ “great tactical ploys of all time” to enter the U.S. “A 200,000-man army, maybe," he reportedly said. "That could be possible.”

On Sept. 10, President Barack Obama directed his administration to admit at least 10,000 Syrian refugees to America over the coming fiscal year, beginning Oct. 1. Secretary of State John Kerry also said last month that the U.S. would considerably increase the number of refugees it takes in over the next two years. He added that 85,000 refugees from across the world would be allowed in the U.S. next year and up to 100,000 in 2017.

A large number of Syrians have left their homes and travelled, risking their lives for better shelter. About 9 million Syrians have been displaced, including over 4 million who fled the war-torn country since March 2011, according to the United Nations.

Former Florida Gov. Jeb Bush, who was holding his own event about an hour away from Trump’s, was asked about the business mogul’s statements on Syrian refugees. Bush said Trump should show "some sensitivity" to something that is a "serious challenge."

"We have an obligation to make sure that people coming here are legitimate, but send them all back? To a hellhole?" Bush said, according to AP. "This is the same guy, by the way, that's also advocating what seems to be support of Putin and his emergence in Syria."

Trump’s comments on Syrian refugees were in stark contrast to what he said last month when asked if migrants travelling into Europe should be allowed in the U.S.

"I hate the concept of it, but on a humanitarian basis, with what's happening, you have to," Trump reportedly said at the time. He also described the migrant crisis as “an unbelievable humanitarian problem.”