The North had earlier Tuesday hinted that it could even reconsider its moratorium on nuclear testing over next month's drills, which have been held for years but were scaled down to facilitate dialogue with Pyongyang.

It was the first statement from the North on the talks since US President Donald Trump and North Korean leader Kim Jong Un agreed to a resumption of dialogue at an impromptu meeting in the Demilitarized Zone in June, following months of deadlock.

Responding to the North's statement, the State Department said it remained upbeat over commitments made by Kim and Trump at a February summit in Vietnam and then during Trump's dramatic walk into North Korea on June 30.

"From our perspective, we would hope that no one would try to block, in their government or our government, the ability for President Trump and Chairman Kim to make progress on the commitments they made to each other in Vietnam," State Department spokeswoman Morgan Ortagus told reporters.

"We look forward, of course, to resuming those negotiations and we hope to talk, always, so we can advance progress on these commitments," Ortagus said.

The joint drills were reduced in scope after Trump's historic first summit with Kim in Singapore last year.

But an unnamed North Korean foreign ministry spokesperson described the drills as "clearly a breach" of a joint statement signed by the leaders in Singapore and hinted that Pyongyang may resume weapons tests in response.

"If the military exercise really goes ahead, it would affect the DPRK-US working-level talks," the official said in comments carried by state news agency KCNA, using the official acronym for North Korea.

Pyongyang's moratorium on nuclear and long-range missile tests was a commitment aimed at improving bilateral relations and "not a legal document inscribed on a paper," the official said.

"With the US unilaterally reneging on its commitments, we are gradually losing our justifications to follow through on the commitments we made with the US as well."

Trump and Kim's unexpected June meeting took place as negotiations between Pyongyang and Washington were at a deadlock, following a rocky negotiation process brokered by Seoul after a thaw in tensions in early 2018.

During the encounter, Trump became the first US president to set foot on the country's soil and the pair agreed to resume working-level talks to lay the groundwork for a future deal.

- 'Very provocative' drills -

There are close to 30,000 US troops stationed in South Korea, and their annual drills with tens of thousands of South Korean soldiers have always infuriated the North -- with Pyongyang condemning the manoeuvres as rehearsals for invasion.

But following the Singapore summit, Trump announced the suspension of what he called Washington's "very provocative" joint military exercises with South Korea.

A smaller-scale version of the exercises was last held in March, with more scheduled for August.

Washington has previously insisted on North Korea's complete denuclearisation as a condition for lifting punishing US sanctions.

At the Singapore summit, the two adopted a vaguely worded statement on "complete denuclearisation of the Korean peninsula" and agreed to "establish new US-DPRK relations".

But the failure to reach an agreement over sanctions relief and what the North was willing to give in return led to the collapse of the leaders' second summit in February in Hanoi.

Tensions were raised in May, during the standstill in negotiations between Trump and Kim, when North Korea fired short-range missiles for the first time since November 2017.

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