Trump went on to suggest that China, which shares a border with North Korea, could do something.
"Perhaps China will put a heavy move on North Korea and end this nonsense once and for all," he wrote.
Trump also tweeted about North Korea late last month, when he acknowledged that China's efforts to "help with North Korea" had "not worked out." Months earlier, he said he discovered that "it's not so easy" for China — North Korea's main trade partner — to rein in the country's leadership.
U.S., South Korean and Japanese officials on Monday said North Korea launched an intermediate-range missile that flew for about 40 minutes and reached an altitude of about 1,500 miles.
North Korea later claimed that the missile was a longer-range intercontinental ballistic missile, which, if confirmed, would be the country's first such test.
ICBMs, which are capable of carrying nuclear weapons, typically have a minimum range of about 3,400 miles. The United States had not confirmed the missile type as of early this morning.
Speaking at a news conference with South Korean President Moon Jae-in on Friday, Trump called the North Korean regime "reckless and brutal" and said its "nuclear and ballistic missile programs require a determined response."
"The era of strategic patience with the North Korean regime has failed. Many years it has failed," he said. "Frankly, that patience is over."
Trump added that the United States is working with South Korea, Japan and other partners "on a range of diplomatic, security and economic measures to protect our allies and our own citizens from this menace known as North Korea."
ABC News' Chris Donovan contributed to this report.