Sen. Lindsey Graham, R-South Carolina, said the United States is "running out of time" when it comes to North Korea and that pre-emptive war is "becoming more likely" as the country's weapons technology "matures."

"We're getting close to a military conflict because North Korea's marching toward marrying up the technology of an ICBM with a nuclear weapon on top that cannot only get to America but deliver the weapon. We're running out of time," Graham said on CBS News' "Face the Nation" Sunday.

"The policy of the Trump administration is to deny North Korea the capability to hit America with a nuclear-tipped missile. Not to contain it," he said. "Denial means preemptive war as a last resort. That preemption is becoming more likely as their technology matures. Every missile test, every underground test of a nuclear weapon, means the marriage is more likely."

His comments came just days after North Korea said it had successfully launched a new type of intercontinental ballistic missile (ICBM), which it claimed is capable of reaching the U.S. The North's state television said the new ICBM was "significantly more" powerful than the previous long-range weapon the country tested.

Graham was critical of Chinese efforts to contain the regime, calling them ineffective. He also said that "if there's an underground nuclear test, then you need to get ready for a very serious response by the United States."

He added, "I think the president, as inherent authority as commander-in-chief, has the ability to strike North Korea to protect the American homeland. But this discussion needs to happen among ourselves."

Graham said he is now urging the Pentagon not to send any dependents to South Korea.

"South Korea should be an unaccompanied tour. It's crazy to send spouses and children to South Korea, given the provocation of North Korea. So I want them to stop sending dependents. And I think it's now time to start moving American dependents out of South Korea," he said.

Graham also issued a warning to President Trump in light of his recent tweets on the FBI and the ongoing special counsel's investigation into Russian meddling in the 2016 presidential election.

"There's an ongoing criminal investigation; Comey may be part of it. You tweet and comment regarding ongoing criminal investigations at your own peril. I'd be careful if I were you, Mr. President. I'd watch this," he said.

Asked if he agreed with the president's assessment that the FBI's reputation is the "worst in history" after being run by former Director James Comey, Graham said he disagreed but still has questions he wants answered.

"I think Comey needs to answer questions as his time as director. I think he made some decisions that, they were really very, very wrong."

In light of Flynn's guilty plea to lying to the FBI as part of the special counsel's investigation, Graham said "what Flynn lied about is not a crime."

"I don't think it's wrong for a transition person to talk to a foreign government about change in policy," he said. "I don't think the Logan Act is worth the paper it's written on. So I'm not really worried about what happened after the election in terms of trying to communicate with the Russians about the Israeli resolution or about sanctions."

He added, "It comes down to the following to me: was there any effort by the Trump campaign to coordinate with Russian intelligence services or any entity controlled by the Russians to receive benefit during the election? And they found the one guy that would know that."

Graham said of Flynn's knowledge, "If there was coordination between the Trump campaign and the Russians, I can't think of a person who would know more about that than Flynn."

"There is no evidence of collusion. Nobody's been charged with it. But you found the one person who would know if it did exist. So it won't be long before we understand, one way or the other, whether Trump people colluded with Russia," Graham said.