"The weapons you are acquiring are not making you safer. They are putting your regime in grave danger. Every step you take down this dark path increases the peril you face," Trump said. "It is not the paradise that your grandfather envisioned. It is a hell that no person deserves."

Tensions have heightened amid North Korea's nuclear and missile tests and exchanges of incendiary rhetoric between Trump and Kim.

The US leader had mocked Kim Jong-un by calling him "Little Rocket Man." He also said he would "totally destroy" North Korea if the US were forced to defend itself and its allies due to the North's nuclear and missile threats.

Seoul's unification ministry said that Trump dialed down his tone, but delivered a message that can be painful for the North Korean leadership.

"North Korea might be pondering over what to do in that it has suspended its provocative acts for about 50 days and Kim Jong-un's public activity has been on the decline (in recent weeks)," a ministry official said. "We are closely watching the North's reaction."

Cheong Seong-chang, a senior research fellow at the Sejong Institute, said North Korea is likely to strongly protest Trump's speech as he called for tougher sanctions and highlighted the North's dismal human rights record.

"North Korea could regard Trump's speech as a declaration of war against it," Cheong said. "I see a high chance of North Korea firing more missiles."

But some experts expect that North Korea is likely to take a wait-and-see approach and decide on its next step after watching the summit between Trump and his Chinese counterpart, Xi Jinping. (Yonhap)