By Kate Sullivan

(CNN) -- Trump declared Sunday morning the United States has not "given up anything" in negotiations with North Korea in response to criticism that Pyongyang is getting more out of the talks than Washington.

"Wow, we haven't given up anything & they have agreed to denuclearization (so great for World), site closure, & no more testing!" Trump tweeted.

The President followed up with a second tweet that said, "We are a long way from conclusion on North Korea, maybe things will work out, and maybe they won't -- only time will tell."

Trump was responding to comments by Chuck Todd on NBC's "Sunday Today" show in which he said North Korean leader Kim Jong Un "seems to be giving very little but making it seem like he's giving a lot."

Todd said the tone of cooperation was a positive development but added, "there's not many preconditions the United States is asking for."

"So far in this potential summit, North Koreans have gotten a lot out of it," Todd said, adding that Washington has not negotiated the release of Americans being held captive in North Korea and that Kim Jong Un has not pledged to denuclearize, he said.

"There's a lot of things they are not promising that is raising some red flags," Todd said.

North Korea said its quest for nuclear weapons is complete and it no longer needs to test its weapons capability, a significant change in policy for Kim, who has relentlessly pursued nuclear and ballistic weapons as a means to ensure the regime's survival.

Kim said Saturday that "under the proven condition of complete nuclear weapons, we no longer need any nuclear tests, mid-range and intercontinental ballistic rocket tests, and that the nuclear test site in northern area has also completed its mission," according to the state-run Korean Central News Agency, or KCNA.

Analysts stressed caution over Kim's words, noting that Pyongyang must be seeking something in return and can always go back on its word.

Josh Pollack, senior research associate at the Middlebury Institute of International Studies at Monterey, California, said the news was Kim's way of announcing his country is a fully paid-up member of the nuclear club.

"They have wanted to be seen as an arrived nuclear power for a while, and one thing that the other nuclear powers don't do is test. With the exception of India and Pakistan, no one has done it since 1996, so it's a sign of immaturity to test and they're saying: 'We're technically mature now, so we don't need to (test) anymore.'

"They're not giving anything up, they're keeping (their weapons), and that's the message," he said. "It was wrapped in this seeming concession, but it's not really a concession. (If) they can decide to test after all, they can just start doing it again."

Republican Sen. Bob Corker, of Tennessee, said Sunday on CNN's "State of the Union," that Kim is making a "good public relations move" and everyone within Congress and the administration "approaches this with skepticism and caution."

Corker pointed out that Kim did not pledge to denuclearize "on the front end," and he could easily start testing missiles again.

Corker said he does not think Washington should make an agreement that does not include North Korea's complete denuclearization, noting "denuclearization has been our policy for years."

But negotiations are just beginning, and "we have no idea where this is going to go," he said.

"This has been a 25-year saga" with the North Korean regime, Corker said, but he added that he is glad the meetings are taking place.

White House counselor Kellyanne Conway also weighed in on North Korea on "State of the Union," referring to the Senate's consideration of Trump's pick for secretary of State, current CIA DIrector Mike Pompeo.

Trump "needs his new secretary of state confirmed so the chief diplomat can go back over to North Korea and elsewhere to sit down and try to denuclearize the Korean peninsula, which is in everybody's interest," she said.

The-CNN-Wire

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