French rescuers said Friday they were unable to find the possible sign of life they detected a day earlier under the rubble of a hotel that collapsed in the earthquake a week ago on Indonesia's Sulawesi island.

The five-member team from French organization Pompiers de l'urgence said late Thursday its life-searching sensor "detected the presence of a victim" under thick concrete in the wreckage of the Mercure Hotel in Palu. The device can pick up breathing and heartbeats, but the team also cautioned gas leaks and other factors can result in false positives.

The team stopped digging overnight. But after an hour of searching Friday morning, team member Philip Besson said they couldn't find the signal again.

"We strongly believed in it yesterday. Now we have nothing at all ... we tried everything and have no response," he said.

Local rescuers were continuing to dig at the site.

The death toll from Friday's 7.5 magnitude earthquake that spawned a tsunami has risen to 1,558, with scores more believed buried in deep mud and under debris of collapsed buildings and homes.