New restrictions on immigrants and refugees will mean legal permanent residents, also known as green cards holders, from Syria and six other Muslim-majority countries will have to be cleared into the United States on a case-by-case basis, a senior US administration official said on Saturday.

In a briefing with reporters, officials defended the scope and execution of the new executive order signed by President Donald Trump on Friday, a move that has caused chaos and alarm at airports.

Asked about lawsuits filed against the order, the officials declined specific comment, but said foreigners do not have a right to enter into the United States, and dismissed as "ludicrous" the notion that the move amounted to a "Muslim ban."

An official said Afghanistan, Malaysia, Pakistan, Oman, Tunisia and Turkey were Muslim-majority countries not included in the order.