Syria has become the world's worst refugee crisis in more than 20 years, the U.N. High Commissioner for Refugees (UNHCR), Antonio Guterres said Tuesday, with more than 6,000 people fleeing the country every day.

"We have not seen a refugee outflow escalate at such a frightening rate since the Rwandan genocide almost 20 years ago," Guterres told a U.N. Security Council briefing.

U.N. Assistant Secretary General for Human Rights Ivan Simonovic said the new numbers represent "a drastic deterioration of the conflict."

About 1.8 million Syrian refugees are registered with the UNHCR in Lebanon, Jordan, Turkey, Iraq and Egypt, and two-thirds of them have arrived since the beginning of this year. The real numbers, however, are likely much higher.

Valerie Amos, the undersecretary general for Humanitarian Affairs and Emergency Relief Coordinator, said 6.8 million Syrian refugees are in need of urgent humanitarian assistance, including more than 4.2 million internally displaced people. Amos said the U.N. needs another $3.1 billion to make it through the end of the year.

The world is "not only watching the destruction of a country but also of its people," Amos said. "The security, economic, political, social, development and humanitarian consequences of this crisis are extremely grave and its human impact immeasurable in terms of the long-term trauma and emotional impact on this and future generations of Syrians."

The U.N. announced last month nearly 93,000 people had been killed since the conflict began in March 2011, including more than 6,500 children.