GENEVA — The number of refugees from the Syrian civil war has risen above three million, the United Nations refugee agency said Friday, calling the crisis “the biggest humanitarian emergency of our era.”

More than a million people have fled in the last 12 months alone, the refugee agency said, counting only those who registered as refugees. The total number is believed to be significantly higher. Countries surrounding Syria that have borne the brunt of the exodus estimate that several hundred thousand more Syrians have escaped across their frontiers seeking safety.

Lebanon, with a population of less than five million, has taken in more than 1.1 million Syrian refugees, while Jordan has 608,000 and Turkey 815,000, according to the agency, the Office of the United Nations High Commissioner for Refugees. Tens of thousands more fled to Iraq over the past three years only to face new dangers from the onslaught of Islamic militants based in Syria.

“Almost half of all Syrians have now been forced to abandon their homes and flee for their lives,” the refugee agency said in a statement, noting that another six and a half million Syrians in the country had also been displaced in warfare between the government of President Bashar al-Assad and various rebel forces.