The unevenness of aid reaching post-earthquake Haiti weakens confidence in the United Nations' ability to deliver relief, the organization's relief chief said.

A confidential e-mail sent by John Holmes, head of the U.N. Office for the Coordination of Humanitarian Affairs, criticized U.N. managers for failing to adequately oversee the relief effort in Haiti following a devastating earthquake Jan. 12, The Washington Post said. The newspaper obtained a copy of the e-mail.

The e-mail focused on the slow implementation of the organization's humanitarian strategy of assigning key U.N. relief agencies the responsibility for coordinating delivery of basic needs in 12 areas.

A "lack of capacity has meant that several clusters have yet to establish a concise overview of needs and develop coherent response plans, strategies and gap analyses," Holmes said in the e-mail. "This is beginning to show and is leading others to doubt our ability to deliver."

Despite his harsh words, Holmes acknowledged the relief community has "achieved a great deal in Haiti."

Officials told the Post 3.4 million people have been fed through the U.N. World Food Program and more than 850,000 get daily 1.3-gallon rations of water.