Police in South Africa were combing a township tavern for evidence on Monday after the mysterious death of 21 teenagers after a night out. Most of the victims, some as young as 13 years, were found dead inside a popular bar in the southern city of East London. Some died later in hospital.

They bore no visible signs of injury, sparking speculation among local officials and politicians that this was a case of under-age drinking that went tragically wrong. Special investigators from Pretoria have been rushed to the scene.

“The detectives will be resuming their work at the crime scene today,” regional police spokesman Thembinkosi Kinana told journalists.

Many of the victims are thought to have been students celebrating the end of their high-school exams, officials said.

Autopsies are being conducted to see if the deaths could be linked to poisoning.

“Post-mortems (were) completed by last night and the bodies will be released to their families today,” said Yonela Dekeda, provincial spokeswoman for the health department.

Forensic analysis will be conducted this week.

“Samples were taken and were on first flight today to Cape Town, where the tests will be conducted,” said Unathi Binqose, a government official on safety.

Drinking in South Africa is permitted for over-18s. But in township taverns which are often located cheek-by-jowl with family homes, safety regulations and drinking-age laws are not always enforced.

President Cyril Ramaphosa is among those who have voiced concern. The teenagers reportedly “gathered at a venue which, on the face of it, should be off-limits to persons under the age of 18,” he said.