This May 17, 2014 picture released from Korean Central News Agency (KCNA) on May 18, 2014 shows a construction division officer (top) apologising to residents following the May 13 accident in the construction site of an apartment house in Pyongyang.
South Korea offered its condolences to North Korea on Tuesday over the deadly collapse of a Pyongyang apartment building that led to a rare apology from the secretive hardline state.
The Koreans have been locked in an escalating war or words lately over the origin of spy drones but both have still managed to send messages of condolence at times of tragedy.
Seoul's Unification Ministry said it had sent its "deep condolences" to the North over last Tuesday's collapse.
South Korean officials have said the incident involved a 23-storey block in Pyongyang's Pyongchon district, which housed almost 100 families.
On Sunday, senior North Korean officials publicly apologised for the "unimaginable" accident at the apartment complex, which was still being built.
The North's state media blamed "irresponsible" supervision by officials in charge of construction and gave no figures of the numbers to have died.
However, South Korean officials said more than 90 families already had been in residence.
Seoul's message was sent through a Red Cross channel which handles cross-border communications and comes a month after the North voiced its condolences over a ferry disaster in the South which claimed around 300 lives.
North and South Korea remain technically in a state of war, but declarations of sympathy at times of national grief are not unprecedented.
The two Koreas have upped the rhetorical ante in their verbal exchanges this month over crashed surveillance drones recovered on the South Korean side of the border.
Seoul said a joint investigation with US analysts had provided "smoking gun" evidence that the drones came from the North. Pyongyang flatly denied its involvement.