The United States is prepared to "ratchet up" pressure on North Korea after its latest provocations but remains open to talks, US Secretary of State John Kerry said Monday.

"It is still possible we will ratchet up (the pressure) even more depending on the actions of the DPRK (North Korea)," Kerry told reporters after a G7 meeting in Hiroshima.

"But we have made it clear... we are prepared to negotiate a peace treaty" on the Korean peninsula, he said, repeating that such a move would depend on North Korea's denuclearisation.

Kerry had said in February that a denuclearised North Korea could one day enter talks with Washington on a treaty formally ending the Korean War of 1950-53.

The conflict ended with an armistice and not a peace treaty. The US insists that Pyongyang must denuclearise as a condition for talks on a peace pact.

The State Department confirmed in February that Pyongyang had reached out to Washington in a tentative bid to discuss a treaty, but said its January nuclear test had derailed the initiative.

The North said Saturday said it had successfully tested an engine designed for an inter-continental ballistic missile that would "guarantee" an eventual nuclear strike on the US mainland.

It was the latest in a series of claims of significant breakthroughs in nuclear weapons and ballistic missile programmes.

Source: AFP