Valerie Amos, UN under secretary general for humanitarian affairs, said she had expected aid had been delivered to survivors in even the most remote islands after the November 8 disaster.
But she added: "Although we've got significant aid now coming in to the major centres, we still have a little bit of a worry that in a couple of the smaller islands there may be needs there that we haven't managed to meet yet.
"I'm still hearing worrying reports where people said they hadn't received any aid as yet, and we're looking into that."
Typhoon Haiyan and its tsunami-like storm surge ploughed through Tacloban and other coastal areas, leaving more than 5700 dead and more than 1700 missing throughout the region. About four million people were displaced.
Baroness Amos defended the Philippine government against criticisms that it had been too slow to deliver aid to victims.