Fighting between Syrian troops and rebels in the country's largest city, Aleppo, has forced 200,000 people to flee the area over the past two days.
Valerie Amos said in a statement Sunday the fighting is making it hard for humanitarian agencies to provide displaced residents with urgently needed food, mattresses, blankets, hygiene supplies and drinking water.
Also Sunday, Jordan opened its first official tent camp for refugees from neighboring Syria. Foreign Minister Nasser Judah said Jordan has taken in 142,000 Syrians, with up to 2,000 more arriving each day.
Turkey has been sheltering more than 44,000 Syrians.
Syrian activists said security forces fired tank shells and artillery against rebel positions in Aleppo Sunday.