Denmark has put using AstraZeneca's COVID-19 vaccine shots on hold for two weeks after reports of cases of blood clots forming, including one death in Denmark, Danish authorities said on Thursday.

They did not say how many reports of blood clots there had been, but Austria has stopped using a batch of AstraZeneca shots while investigating a death from coagulation disorders and an illness from a pulmonary embolism.

"Both we and the Danish Medicines Agency have to respond to reports of possible serious side-effects, both from Denmark and other European countries," the director of the Danish Health Authority, Soren Brostrom, said in a statement.

"It is currently not possible to conclude whether there is a link. We are acting early, it needs to be thoroughly investigated," Health Minister Magnus Heunicke said on Twitter.

The vaccine would be suspended for 14 days. The health agency did not give details of the Danish blood clot victim.

AstraZeneca on Thursday told Reuters in a written statement the safety of its vaccine had been extensively studied in human trials and peer-reviewed data had confirmed the vaccine was generally well tolerated.

The drugmaker said earlier this week its shots were subject to strict and rigorous quality controls and that there had been "no confirmed serious adverse events associated with the vaccine." It also said it was in contact with Austrian authorities and would fully support their investigation.

The European Union's drug regulator, the European Medicines Agency (EMA), said on Wednesday there was no evidence so far linking AstraZeneca to the two cases in Austria.

It said the number of thromboembolic events — marked by the formation of blood clots — in people who have received the AstraZeneca vaccine is no higher than that seen in the general population, with 22 cases of such events being reported among the 3 million people who have received it as of March 9.

EMA was not immediately available for comment on Thursday.

Four other countries — Estonia, Lithuania, Luxembourg, and Latvia — have stopped inoculations from the batch while an investigation continues, the EMA said.

The batch of 1 million doses went to 17 EU countries.

The Danish Medicines Agency said it had launched an investigation into the vaccine together with corresponding agencies in other EU-countries as well as the EMA.

"It is important to emphasize that we have not opted out of using the AstraZeneca vaccine, but that we are putting it on hold," Brostrom said.

So far, 136,090 Danes have received a shot with AstraZeneca's vaccine in a country of 5.8 million. The Nordic country also uses vaccines from Pfizer-BioNTech and Moderna

Denmark's Health Authority said it had pushed back the final date for when it expects all Danes to have been fully vaccinated by four weeks to Aug. 15 as a result of the vaccine suspension.

Spain On Thursday said it had not registered any cases of blood clots related to AstraZeneca's vaccine so far and would continue administering the shots.