Amos urged donors to help, saying she hoped a Wednesday conference in Kuwait would yield some of the $1.5 billion in aid requested by humanitarian groups.
That money would help Syrians displaced within their own country and those who have fled to neighboring nations for six months, she said.
"If we do not receive these funds, we will not be able to reach the poorest and most vulnerable families who so desperately need our help," she said.
Zaatari is in Jordan's northern desert, northeast of Amman.
Enterprising Syrian refugees, many of whom arrived with nothing, have set up their own retail avenue amid dusty tents and prefabricated metal shelters. The facilities are providing a small source of income and -- perhaps more importantly -- something to do to stave off the boredom and discomfort of camp life.
The United Nations estimates 60,000 people have died in nearly two years of fighting between the rebels and government forces.
Violence continued in Syria on Friday, with three people killed in clashes nationwide, according to the opposition Local Coordination Committees. Heavy shelling continued in the Damascus suburbs, the group said.
Elsewhere, rebels raided the Idlib Central Prison and freed 300 prisoners, the LCC said.
Video purportedly taped by rebels showed them using pipes to pry the prison's barred windows away from the wall.
"Be patient, be patient," a man behind the camera shouts at the inmates, with one waving his hand out the cell bars.
Rebels were engaged in firefights Friday with government security forces at the prison, and the rebels managed to cross some prison walls, the Syrian Observatory for Human Rights said.
Freed, wounded prisoners and injured rebels were treated at a makeshift clinic in Amaaret Misreen about 6 miles (9 kilometers) outside Idlib, an opposition activist said.
The rebels' assault on the prison began Friday and they were in control of 60% of the facility, though fighting continued over two major buildings, said opposition activist Omar Abu Al-Huda. He told CNN he witnessed the offensive.
The inmate population includes political prisoners, and the prison is considered the last major government position in western Idlib, Al-Huda said.
Government forces have an army position, with tanks and heavy machine guns, inside the prison.
CNN cannot independently verify many claims from Syria, as the government has severely restricted access by international journalists.
On Monday, representatives from 50 countries and organizations will meet in Kuwait with two vice presidents of the National Syrian Coalition, a spokesman with the French Foreign Ministry said.
The meeting will be a follow-up to a December 12 gathering in Marrakech, Morocco, where United States, Britain, France, Turkey and the Gulf Cooperation Council recognized the opposition coalition, the spokesman said.
The meeting will address greater recognition for the coalition, confirmation of financial pledges to it, and the humanitarian situation in Syria, the spokesman said. Refugee camps in neighboring countries will also be discussed, the ministry said.