She did not say why the trucks had not been able to cross into Gaza from Egypt on Tuesday.
The United States is negotiating with Israel, Egypt and the United Nations to try and create a delivery mechanism to get aid into Gaza.
They are wrangling over procedures for inspecting the aid and bombardments on the Gaza side of the border.
Since limited aid deliveries began on Saturday, 54 trucks have crossed into Gaza carrying food, medicine and water, which U.N. Secretary-General Antonio Guterres described as "a drop of aid in an ocean of need."
Senior U.N. aid official Lynn Hastings had earlier told the Security Council that 20 trucks were due to cross on Tuesday.
Persons:
Khan Younis, Abu Mustafa, Joe Biden, Eri Kaneko, Biden, Antonio Guterres, Lynn Hastings, John Kirby, Hastings, Michelle Nichols, Ismail Shakil, Deepa Babington
Organizations:
United Nations, REUTERS, UNITED NATIONS, White, Security Council, White House, Thomson
Locations:
Gaza, Egypt, United States, Israel, Rafah