"Twenty people lost their lives and 93 others wounded in the blast that hit a hospital in Qalat city today morning," provincial government spokesman Gul Islam Seyal told Xinhua news agency.
The attack occurred at around 6 a.m. in the city of Qalat, capital of insecure Zabul province, the spokesperson of the governor of the region, Seyal, told Efe news.
He said the "powerful bombing badly destroyed the hospital building and several nearby houses".
Most of the victims were "hospital health workers, patients and civil from nearby houses", he said, adding that the number of victims could rise in the next few hours.
The injured were evacuated to other Qalat hospitals and to the neighbouring city of Kandahar.
Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack and said it was directed against a National Security Directorate (NDS) building.
"Due to the attack most of the buildings and facilities (were) destroyed. A big number (of) intelligence officers, soldiers and employees killed and injured," Mujahid said in a statement.
Seyal however, rejected the Taliban claim, saying all the victims killed in Qalat's attack Thursday morning were innocent civil.
There has been a surge in militant attacks in Afghanistan in the past few weeks ahead of the presidential election on September 28.
( With inputs from IANS )