More than three million Syrian refugees have fled the civil war ravaging their country and have become registered in neighboring countries as of Friday, a million of them in the past year alone, the United Nations said on Friday. However the exodus, which began in March 2011, shows no signs of abating.

Pointing to reports of "increasingly horrifying conditions inside the country" as an explanation of the surge, UNHCR claimed that the number of registered Syrian refugees was only at two million less than a year ago, Reuters reported.

"The Syrian crisis has become the biggest humanitarian emergency of our era, yet the world is failing to meet the needs of refugees and the countries hosting them," Antonio Guterres, U.N. High Commissioner for Refugees, said in a statement.

A further 6.5 million are reported to be displaced within Syria, meaning that "almost half of all Syrians have now been forced to abandon their homes and flee for their lives", the UN's refugee agency said in a statement, adding that the number did not include hundreds of thousands of others who fled without registering as refugees.

While the highest concentrations remain in neighboring countries of Lebanon (1.14 million), Turkey (815,000) and Jordan (608,000), some 215,000 refugees are in Iraq with the rest in Egypt and other countries, UNHCR said, describing "cities where populations are surrounded, people are going hungry and civilians are being targeted or indiscriminately killed."

In addition, the host governments estimate that hundreds of thousands more Syrians have sought sanctuary in their countries without formally registering, the agency said, adding that most families arrive in a shocking state. "Most have been on the run for a year or more, fleeing from village to village before taking the final decision to leave."

Since the war erupted in March 2011, the increasingly fragmented conflict raging in Syria has claimed more than 191,000 lives, Agence France-Presse reported. With nearly 50 percent of all Syrians being forced to flee their homes, over half of those have been children, UNHCR said.

Meanwhile, "Syrians now constitute the world's largest refugee population under the care of the UNHCR, second only in number to refugees in the decades-old Palestinian crisis that falls under the mandate of a separate U.N. agency UNRWA," according to Reuters.

"The three million refugees from the Syria conflict represent three million indictments of government brutality, opposition violence and international failure," David Miliband, former British foreign secretary and the current head of the International Rescue Committee, said in a statement.

"This appalling milestone needs to generate action as well as anger," he said, also calling for "greatly increased efforts" to reduce the suffering of civilians left inside Syria.