German Health Minister Jens Spahn on Wednesday stated Russia's COVID-19 vaccine had not been satisfactorily tested, including the goal would be to have a safe product instead of simply being first to start vaccinating people.

President Vladimir Putin declared on Tuesday that Russia had become the first country to grant regulatory approval to a COVID-19 vaccine following less than two months of individual testing.

Moscow's decision to give approval before closing trials have been completed has increased concerns among some experts.

"It may be dangerous to start vaccinating millions, if not billionsof people too early since it could kill the acceptance of vaccination if it goes wrong, so I am quite sceptical about what's going on in Russia," Spahn told tv broadcaster Deutschlandfunk.

"I would be pleased if we had a very first, good vaccine but based on what we know - and that's the basic problem, namely that the Russians aren't telling us much - that has not been satisfactorily tested," he added.

Spahn said it was critical, even during a pandemic, to take out appropriate studies and tests and create the results public to give people confidence in the vaccine.

"It's not about being first somehow - it's about having a powerful, analyzed and therefore safe vaccine," he said when asked about Russia's vaccine, which is called"Sputnik V" in homage to the world's first satellite launched by the Soviet Union.

Only about 10 percent of clinical trials are successful and some scientists fear Moscow may be placing national prestige before safety.

Putin and other officials have said it's completely safe. Mass roll-out in Russia is expected to begin in October.