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President Obama's calls for more "openness" to refugees fleeing the war-torn Middle East are "disgraceful," Donald Trump said on "Fox and Friends" this morning.

Trump said it's inconceivable that the president - who made the comments in his weekly address on Saturday - is actually calling for "open borders" in the wake of the terror attack in Brussels.

"You would almost say it's disgraceful," Trump said. "You can't even imagine that a man could make those statements, especially a president of this country."

He said recent events around the world prove just how much we need border security, including a wall along the U.S.-Mexico border.

The Republican presidential front-runner pointed out that Middle Eastern refugees, in particular, are undocumented, with no way for immigration officials to verify who they are and where they're coming from.

"In terms of security, this open door policy is catastrophic ... This could lead to the downfall of the greatest nation on Earth."

Watch more from Trump above.

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