SEOUL – North Korea's top military body lashed out Thursday at an ongoing South Korea-US army drill, warning that it could compromise a recent easing of military tensions on the Korean peninsula.

The criticism from the North's National Defence Commission marked the first high-level rebuke of the 10-day Ulchi Freedom Guardian joint exercise, which ends on Friday.

Pyongyang's unusual silence over an annual drill that it habitually condemns as a war rehearsal had been attributed to ongoing North-South talks on a number of cross-border projects.

Thursday's statement was forthright but lacked the bellicose rhetoric of similar denunciations issued during the heightened tensions of March and April.

The powerful commission, chaired by North Korean leader Kim Jong-Un, accused South Korea and the United States of playing "a dangerous war game" and making provocative "nuclear threats" towards Pyongyang.

"The hard-won mood of reconciliation is now faced with a grave challenge posed by... the US and South governments that haven't shed their old-fashioned confrontational approach," it said in a statement carried by the state-run Korean Central News Agency.

The Ulchi Freedom Guardian exercise practises a joint response to a North Korean invasion. Although largely played out on computers, it involves more than 80,000 South Korean and US troops.

The North's muted response to the drill, which started at the beginning of last week, reflected progress in cross-border talks on a number of key issues.

The two Koreas recently agreed to work together to reopen their shuttered Kaesong industrial complex and to hold a family reunion event for those separated during the Korean War.

But Pyongyang was frustrated this week by Seoul's lukewarm response to its proposal for parallel talks on resuming South Korean tours to its Mount Kumgang resort – a source of badly-needed hard currency.

The Seoul-invested resort was closed in 2008 after a South Korean tourist was shot dead by a North Korean soldier.

North Korea was also angered by South Korea's hosting last week of a UN Commission of Inquiry into the North's human rights record.

Pyongyang described North Korean defectors who provided harrowing testimony to the commission as "human scum" manipulated by the South's authorities.

"There is a limit to our magnanimity and patience," the defence commission warned Thursday.