Nine coronavirus patients died Monday in Russia's republic of North Ossetia after an oxygen pipe ruptured at a hospital in the capital Vladikavkaz, authorities said.

"Nine patients with coronavirus died due to the lack of oxygen at the Republic Clinical Hospital of Vladikavkaz," Russian news agencies cited the ministry as saying. 

They also quoted the republic's acting head Sergei Minyaylo as saying "there was a rupture of the oxygen pipe" and "the oxygen supply was interrupted".

The TASS news agency cited the Investigative Committee, which probes major crimes in Russia, as saying that a criminal case had been launched into the provision of services that do not meet safety requirements and result in deaths by negligence.  

The health ministry said 71 patients were in intensive care at the time of the accident, including 13 supported by "mechanical ventilation".

All nine patients who died were on ventilators, it said.

Minyaylo said the lungs of the nine patients had already suffered "90 percent damage" before the pipeline ruptured and that it was too early to blame their deaths on the accident.

He said that the problem was "promptly detected and eliminated within 30 to 40 minutes" and the rest of the patients were transferred to "oxygen cylinders and backup oxygen sources".

He added that the North Ossetia republic in Russia's North Caucasus region has no problem supplying its hospitals with oxygen.

Russia has seen a number of accidents in its coronavirus hospitals lead to the deaths of patients during the pandemic. 

In June, three people died in a fire at a hospital in the Russian city of Ryazan southeast of Moscow, with a faulty ventilator believed to be the cause of the blaze. 

Several people also died in May last year in fires at hospitals in Moscow and Saint Petersburg, with faulty ventilators likewise believed to have sparked the blazes.

Russia is the world's fourth worst-hit country in terms of coronavirus cases with nearly 6.5 million registered, according to an AFP tally. 

With 165,650 deaths from the virus, Russia has the highest official Covid-19 toll in Europe -- even as authorities have been accused of downplaying the severity of the outbreak. 

Under a broader definition for deaths linked to the coronavirus, statistics agency Rosstat said Russia had seen at least 290,000 fatalities as of the end of May.