The conflict between opposition fighters and regime forces has turned Syria into one of the world's worst humanitarian crises, exacerbated by attacks on aid workers, U.S. officials said Tuesday.
"There are 2.5 million people in need of aid now inside Syria, and 1.2 million have been displaced from their homes, so on that scale it's right up there with the worst crises in the world today," said David Robinson, a top official at the State Department's Bureau of Population, Refugees and Migration.
The United States is spending $82 million (66 million euros) on food and medical aid for Syria that is being delivered "through a variety of networks", said Mark Bartolini, director of the office of U.S. Foreign Disaster Assistance.
The U.S. officials were speaking in a joint online press conference.
Bartolini said no U.S. aid personnel were on the ground and that the aid was being delivered "through a variety of networks" which he declined to describe because of what he said were "widespread" attacks on aid workers and clinics.
"It's like nothing I've seen in any conflict I've ever been involved in, the level of attacks against people simply trying to provide humanitarian assistance," said Bartolini.
Asked who was carrying out the attacks, he said that most happened in locations in opposition-held areas, "so I think you can draw your own conclusions as to who is carrying them out".
Medical charity Doctors Without Borders (Medecins Sans Frontieres - MSF) meanwhile said Tuesday that for the last two months it had been running a small hospital in a rebel-held area of northern Syria.
The center has so far carried out 300 operations on wounded fighters and civilians, currently has 12 beds and can be enlarged to host 30 beds, MSF chief Filipe Ribeiro told reporters in Paris.
He said the hospital, run by seven foreign doctors and around 50 Syrian staff, had been declared illegal by the Syrian regime when MSF informed them of its presence.
Syria's popular uprising has spiraled into an armed conflict with some 23,000 deaths since March last year, according to the Syrian Observatory for Human Rights. The United Nations puts the death toll at 17,000.