GENEVA, April 13 (Reuters) - The World Health Organization, asked about reports of rare blood clots after vaccination with the Johnson & Johnson COVID-19 shot, told Reuters on Tuesday (Apr 13) that it was awaiting reviews by the US and European regulators and monitoring global data.

"We're watching closely, waiting for EMA (European Medicines Agency) and FDA (US Food and Drug Administration) reviews and monitoring the global database of adverse event reports to see if there have been cases anywhere else," the WHO said in an email reply.

"It will take a little time to review the data."

US federal health agencies on Tuesday recommended pausing the use of Johnson & Johnson's COVID-19 vaccine after six women under 50 given the shot developed rare blood clots.

Following the news, Johnson & Johnson said it was delaying the rollout of the vaccine to Europe, a week after regulators there said they were reviewing rare blood clots in four recipients of the shot in the United States.

The moves come after European regulators said earlier this month they had found a possible link between AstraZeneca's COVID-19 vaccine and a similar rare blood clotting problem that led to a small number of deaths.

Johnson & Johnson's single dose vaccine - most COVID-19 shots are delivered over two doses - and AstraZeneca's low-cost vaccine are seen as vital tools in the fight against a pandemic that has claimed more than 3 million lives.

Immunology experts stressed the risk posed by the Johnson & Johnson vaccine appeared extremely low, and that the shot remained a valuable tool against the risks of COVID-19.

However, they acknowledged the need for health officials to proceed with caution to understand the best ways to mitigate any risk.