With the exception of the International Committee of the Red Cross, aid agencies face many restrictions in their efforts to transport food and supplies to civilians caught up in the conflict.
Clinton "offered immediate and post-conflict reconstruction assistance," the statement said.
She also condemned the rebel actions toward civilians.
Human Rights Watch has accused the Tamil Tigers of holding civilians as "human shields," preventing people from leaving the areas under their control and forcibly recruiting children to fight the army.
Duguid said Clinton urged Rajapaksa to "devise a political solution" to the conflict.
"The United States believes that a durable and lasting peace will only be achieved through a political solution that addresses the legitimate aspirations of all of Sri Lanka's communities," he said.
"We call on the Sri Lankan Government to put forward a proposal now to engage Tamils who do not espouse violence or terrorism, and to develop power s