U.S. federal health agencies on Tuesday recommended pausing use of Johnson & Johnson's COVID-19 vaccine for at least a few days after six women under age 50 developed rare blood clots after receiving the shot, dealing a fresh setback to efforts to tackle the pandemic.

Johnson & Johnson said it would delay 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. South Africa also suspended use of J&J's vaccine.

Acting U.S. Food and Drug Administration Commissioner Janet Woodcock said the agency expected the pause to be a matter of days, and was aimed at providing information to healthcare providers on how to diagnose and treat the clots.