"The poor people here in Gaza don't feel the benefits of the truce and their living conditions continue to deteriorate as Israel still doesn't allow all kinds of basic goods and food supplies into Gaza," John Ging, the agency's director of operations, said.
He said that Israeli supplies only 25% of the goods that the enclave of 1.5 million people needs.
The international relief organization announced on Wednesday that it would provide $6.5 million in urgent aid to 92,000 of Gaza's poorest residents.
The Gaza Strip, one of the world's most densely populated areas, has been blockaded by Israel since the hard-line Islamic movement Hamas seized control of Gaza from Palestinian President Mahmoud Abbas' Fatah movement in June 2007.
Israel and Hamas-led militants reached a truce agreement on June 19. Under the deal, Israel agreed to reopen its border crossings with the Gaza Strip to allow the supplies of essential goods into the Palestinian territory.
Since then, Gaza militants have repeatedly launched rocket attacks on Israeli territory - Israel reclosed the border crossings in response.