As tensions continued to mount on Thursday between Washington and Pyongyang, former President Jimmy Carter said North Korean leaders are convinced the U.S. plans to launch a preemptive strike against the nation.

“I have visited North Korea three times, and have spent more than 20 hours in discussions with their political leaders regarding important issues that affect our relations,” Carter said in a statement. “During all these visits, the North Koreans emphasized that they wanted peaceful relations with the United States and their neighbors, but were convinced that we planned a preemptive military strike against their country.”

Carter said North Korea wants a new peace treaty to replace the ceasefire agreement that’s existed since the end of the Korean War in 1953, and to end economic sanctions.

“They have made it clear to me and others that their first priority is to assure that their military capability is capable of destroying a large part of Seoul and of responding strongly in other ways to any American attack,” Carter said.

Carter also said China’s influence of China in Pyongyang “seems to be greatly reduced since Kim Jong Un became the North Korean leader in December 2011.”

On Thursday, President Donald Trump doubled down on his threats to unleash "fire and fury" on North Korea, pushing back against criticism that his aggressive rhetoric might backfire and inflame tensions.

“Maybe it wasn’t tough enough," Trump said of his previous statement. "It's about time that somebody stuck up for the people of this country and for the people of other countries.

Trump said he would consider negotiations with North Korea and declined to discuss the possibility of a preemptive strike against Pyongyang.

Trump spoke at his Bedminster National Golf Club after meeting with Vice President Pence, Chief of Staff John Kelly and National Security Adviser H.R. McMaster.

The president's comments come two days after he threatened to unleash "fire and fury" on North Korea if the rogue nation persists in threatening the United States.

Yet North Korea's top general escalated those threats, saying this week he was drawing up plans to attack the U.S. territory of Guam with four ballistic missiles.

“The harsh rhetoric from Washington and Pyongyang during recent months has exacerbated an already confrontational relationship between our countries, and has probably eliminated any chance of good faith peace talks between the United States and North Korea,” Carter said. “Our leaders need to encourage talks between North Korea and other countries, especially China and Russia. The recent UN Security Council unanimous vote for new sanctions suggests that these countries could help.

“In all cases, a nuclear exchange must be avoided. All parties must assure North Koreans we will forego any military action against them if North Korea remains peaceful.”

USA Today contributed to this report.