Countries should not stop using AstraZeneca's Covid-19 vaccine over fears it causes blood clots as there is no indication this is true, the World Health Organization says.
Bulgaria, Denmark and Norway are among the countries that have paused its use.
But on Friday a WHO spokeswoman said there was no link between the jab and an increased risk of developing a clot.
Margaret Harris said it was an "excellent vaccine" and should continue to be used.
Around 5 million Europeans have already received the AstraZeneca jab.
There have been about 30 cases in Europe of "thromboembolic events" - or developing blood clots - after the vaccine was administered. There were also reports that a 50-year-old man had died in Italy after developing deep vein thrombosis (DVT).
The WHO is investigating the reports, as it does any safety questions, Ms Harris said.
But no causal relationship had been established between the shot and the health problems reported, she said.
Bulgaria's decision to pause its rollout followed similar steps by Denmark, Iceland and Norway as well as Thailand. Italy and Austria have stopped using certain batches of the drug as a precautionary measure.
"I order a halt in vaccinations with the AstraZeneca vaccine until the European Medicines Agency dismisses all doubts about its safety," Bulgarian Prime Minister Boyko Borisov said.
The European Medicines Agency, the EU's medicines regulator, said earlier there was no indication the jab was causing the blood clots. It also said the number of cases in vaccinated people was no higher than in the general population.
AstraZeneca said the drug's safety had been studied extensively in clinical trials.
Other countries, including the UK, Germany, Australia and Mexico, have said they are continuing their rollout.
While vast numbers of people are being vaccinated at pace around the world, some of them will still get sick with other things unrelated to the vaccine.
These pauses for the AstraZeneca vaccine are not because it is unsafe to give. It's to allow time for experts to explore why a small number of people who were recently give the shot also developed blood clots.
When an illness occurs shortly after vaccination, it is right to question whether the shot might have contributed in any way.
There is no indication or evidence, however, that the vaccine was linked or responsible.
In the UK, more than 11 million people have already received at least one dose of the vaccine and there has been no sign of excess deaths or blood clots occurring. Europe's drug regulator has also backed the vaccine, saying its benefits are clear. Covid can be deadly and vaccination saves lives.