New Zealand Prime Minister Jacinda Ardern announced an immediate ban on all assault weapons, and “military-style semi-automatic weapons,” like the weapons used in last Friday’s attacks on two Christchurch mosques.

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Ardern announced the ban Thursday and said it would be followed by legislation to be introduced next month.

She said the man arrested in the attacks had purchased his weapons legally and enhanced their capacity by using 30-round magazines “done easily through a simple online purchase.”

Ardern said a buyback program will be created to pay owners "fair and reasonable compensation" for the soon-to-be outlawed guns. She said that it will cost New Zealand between $100 million and $200 million and the guns would be destroyed according to NPR.

Unlicensed gun owners would not be prosecuted for any weapon they turn in.

“Amnesty applies ... we just want the guns back,” Ardern said in a press briefing.

“For other dealers, sales should essentially now cease. My expectation is that these weapons will now be returned to your suppliers and never enter into the New Zealand market again,” she said.

Ardern did not say what would happen to those who violate the law.

>> RELATED: Assault weapon vs. assault rifle: What is the difference?

What is an “assault rifle”?

An assault rifle is a rapid-fire, magazine-fed rifle designed for military use. It is a shoulder-fired weapon that allows the shooter to select between semi-automatic (requiring you to pull the trigger for each shot), fully automatic (hold the trigger and the gun continuously fires) or three-shot-burst modes.

What is an "assault weapon?"

Technically, there is no such thing. What’s called an assault weapon (or sometimes an assault rifle) in reports on gun violence is a semi-automatic rifle that looks similar to the assault rifles used by the military. An AR-15 rifle, like the ones that have been used in some mass shootings, is an example of this type of weapon.

What’s the difference between a semi-automatic and an automatic weapon?

An automatic weapon (“assault rifle”) can shoot more than one round when you pull the trigger. A semi-automatic weapon (“assault weapon”) does not.

Automatic weapons have not been used in recent mass shootings. In the shootings in Orlando, Florida; Newtown, Connecticut, and San Bernardino, California, semi-automatic weapons, were the weapons used.

The Associated Press contributed to this report.