South Korea has voiced regret after North Korea offered no response to a proposal for talks on resuming reunions for families separated by the 1950-53 Korean War.

In a cross-border message earlier this week, Seoul's Unification Ministry had suggested working-level talks on Wednesday to work out details for holding a reunion event.

But as of Wednesday morning, the North had yet to respond.

"We find it regrettable that the North is showing such an attitude after the two Koreas have already agreed to hold the family reunion," the Unification Ministry said in a statement.

"The aged members of the separated families are anxiously waiting for a chance to reunite with their relatives," it added.

North Korea unexpectedly announced on Friday that it was willing to hold a reunion event -- the latest in a series of conciliatory gestures from Pyongyang that the South has treated with scepticism.

Pyongyang said the dates could be chosen by the South, which promptly suggested February 17-21 at the North's Mount Kumgang resort.

That would sandwich the gathering between the February 16 birthday of North Korea's late leader Kim Jong-Il -- an important national holiday -- and annual South Korea-US joint military exercises that are scheduled to begin at the end of the month.

"Given the North said we could set the date... we urge the North to accept our proposed dates and respond to the requested working-level meeting as quickly as possible," the Unification Ministry said.

The South-US drills are held every year and are routinely condemned by the North as a rehearsal for invasion.

A reunion event had been planned last September but Pyongyang cancelled at the last minute, and there are concerns it will do the same this time around, citing the military drills as the reason.

Pyongyang has made several demands that this year's exercises be called off.

Seoul and Washington have insisted they will go ahead, but it appears they will be scaled back in an apparent effort to mollify the North.

Last year, Washington put on a show of military might for the exercise, deploying nuclear-capable stealth bombers and an attack submarine in response to sabre-rattling by North Korea.

This time around, there will be no aircraft carrier and no strategic bombers, according to US military officials.

"Every year the scenario is slightly different," one US defence official told AFP, adding that the United States tends to calibrate what ships and aircraft are featured in response to North Korea's behaviour.

The top US envoy on the North Korean nuclear issue, Glyn Davies, was in Seoul Wednesday and underlined US commitment to the "defensive" annual drills.

"Not one country is taking issue with our exercises except one," Davies told reporters.

South Korea hosts 28,500 US soldiers and the United States would assume overall operational command of joint US and South Korean forces if a full-scale conflict with the North broke out.

An extra 800 US troops from the 12th Cavalry Regiment, along with 40 Bradley armoured fighting vehicles and 40 Abrams M1 tanks, began arriving in the South on Wednesday for a nine-month tour.