Chile's mining minister has acknowledged that a problem has stalled the most advanced of three tunnels being drilled to 33 miners trapped underground, and said officials might have to restart the bore hole in another location.
But Laurence Golborne insisted that the setback is within the range of problems foreseen by authorities before the rescue began and does not significantly alter the expected timeline for getting the men out.
Work on boring the hole stopped last week when a drill struck an iron support beam for a mine shaft at about 900 feet, destroying a drill bit. A replacement part was rushed from the United States, but engineers have so far failed to recover all of the broken metal using magnets.
"If we are unable to remove that bit, the hole would not be able to continue," Mr Golborne said.
He said authorities planned three bore-holes from the beginning precisely in anticipation of such problems, and he met with relatives of the miners on Sunday to assure them that the rescue is still on track.
From the time they first made contact with the miners August 22, some 17 days after the massive underground collapse, authorities have said a rescue could take up to four months.
Mining experts have called that timeline conservative, and it apparently takes into account the possibility of setbacks such as the broken drill bit.
Meanwhile a second drill that went off-line on Friday for routine maintenance has now resumed operating,