Talks between Pyongyang and Washington have stalled since a second summit between US President Donald Trump and North Korean leader Kim Jong Un in Hanoi in February collapsed without an agreement.

The pair met again in June in the Demilitarised Zone and agreed to restart working-level dialogue, but those talks have yet to begin.

Meanwhile, North Korea has carried out several short-range missile tests in recent weeks in protest against annual US-South Korea joint military drills that it sees as a rehearsal for invasion.

Stephen Biegun, the US special envoy for North Korea who leads the working-level talks, arrived in Seoul late Tuesday for a three-day trip, and said Washington was "prepared to engage" as soon as it hears from Pyongyang.

But a spokesman for the North's foreign ministry dashed hopes for renewed dialogue on Thursday, attacking a recent mid-range cruise missile test by the US and plans to deploy F-35 fighter jets in the region as "dangerous" moves that can "trigger a new cold war".

"This compels us to weigh a realistic way of turning our attention more to strengthening the physical deterrence," he said in a statement carried by the official Korean Central News Agency.

"We remain unchanged in our position to resolve all issues in a peaceful manner through dialogue and negotiation," he added.

"However, dialogue accompanied by military threats is of no interest to us."

Washington stations nearly 30,000 troops in the South to defend it from its neighbour.

Trump tweeted earlier this month that Kim had sent him a letter -- hand-delivered to him -- in which he expressed hope that talks would resume "as soon as the joint U.S./South Korea joint exercise are over".