(CNN) Donald Trump reacted to a series of bombing threats and attacks over the weekend with a warning on Monday that "this is only going to get worse."
"I think this is something that will maybe get -- will happen perhaps more and more all over the country," Trump told "Fox and Friends." "It's a mess, and it's a shame, and we're going to have to be very tough."
Trump also said he agreed with early reports of a possible foreign connection to the bombings.
"I think there is -- I think there's many foreign connections," he said.
"You have many, many groups, because we're allowing these people to come into our country and destroy our country and make it unsafe for people," the Republican nominee added, arguing that the stricter immigration policies he has proposed would better protect the US from terror.
Trump also took aim at "magazines" and other media that publish instructions on how to make explosive devices, saying, "Those people should be arrested because they are inciting violence."
"So I see the other day, and they're all talking about it so wonderfully because it's called freedom of the press -- where you buy magazines and they tell you how to make the same bombs that you saw. I would -- now people will go crazy, they'll say Trump is against freedom of the press. I'm totally in favor of freedom of the press. But how do you allow magazines to be sold -- these are magazines that tell you, from step one, go to the store and buy such-and-such, right?"
He continued, "Those people should be arrested because they are inciting violence, OK. They are making violence possible. They should be arrested immediately. They have websites that tell how to make bombs, how to make all sorts of things that are totally destructive, and you know where they are coming from, and yet we don't want to touch them because of freedom of speech."