"Deepest sympathies" have been paid to the families of four men killed in the Glesion mining disaster by the Welsh Secretary David Jones.
Charles Breslin, Philip Hill, Garry Jenkins and David Powell died when the Swansea Valley mine flooded last year.
Mr Jones said: "The incident touched the hearts of everyone, not just in Wales, but across the country."
A number of low-key commemorations are due to take place over the weekend to mark the anniversary.
The four men died after the Gleision drift mine flooded on 15 September 2011 after a retaining wall holding back a body of water failed.
Three other miners managed to escape as the flood engulfed the drift mine. Two then helped in the attempt to save their colleagues, while another was taken to hospital.
A public appeal raised more than £1m which is being shared between the families of the miners, with trust funds set up for the four children who are under 18.
In a statement marking the anniversary, Mr Jones said: "Today, my thoughts, prayers and deepest sympathies go out to the families, friends and loved ones of the brave men who tragically lost their lives at the Gleision Colliery last year.
"The incident touched the hearts of everyone, not just in Wales, but across the country."
The Welsh Secretary added that South Wales Police were continuing to investigate the circumstances of the tragedy, in liaison with the Health and Safety Executive.
On Friday, the first minister Carwyn Jones said the tragedy at Gleision "must never be forgotten" and that lessons must be learned so that such events were "consigned to history".
Several low-key commemorations are planned or have taken place to mark the disaster.
A concert was held underground at Big Pit mining museum in Blaenavon on Thursday to remember the victims of colliery disasters, while the Church in Wales said prayers would be said in all its churches on Sunday.
A tribute was being paid to the victims and rescue teams at the miners welfare brass band competition in Porthcawl on Saturday in the form of a minute's silence.
It is understood the families of the miners will mark the day privately.