Other countries could be added to President Donald Trump's executive order banning travelers from seven nations linked to terrorism, White House Chief of Staff Reince Priebus said Sunday.

In an interview with NBC News' "Meet The Press," Priebus said out of 329,000 people from foreign countries entered the United States on Saturday, and 109 were detained.

"It's all done to protect Americans," he said. "President Trump is not willing to get this wrong."

But, he added, "we're concerned about the issue," in answering why countries where more terrorists have been identified than in those now banned — including Saudi Arabia, Egypt and Pakistan — were not included in the executive order.

"Perhaps other countries need to be added going forward," he said. "But in order to pass muster… we included the seven," adding that the nations were first identified by the Obama administration as needing further vetting.

"Perhaps other countries need to be added," he repeated.

Priebus also said green card holders may be subjected to further questioning if they travel to the banned countries at the discretion of customs and border agents.

"Customs and Border Patrol, if they have a person traveling back and forth [from any of the banned nations]… within their discretion they might ask a few more questions," he said. "Most Americans would agree that would be a good thing to do," adding those discretionary questions have "nothing to do with the executive order."