Pakistani flood survivors, already short on food and water, began the fasting month of Ramadan.
The United Nations has warned that the disaster was far from over, saying a dam in the Sindh province could still burst in the next few days.
A spokesman said UN offcials estimated that up to a quarter of the country is or has been affected by the floods.
Pakistani Prime Minister Yousuf Raza Gilani flew to the southwestern Baluchistan province to see flood-hit areas.
He said: "No one should feel that the relief provided by donors might be misused. Of this I want to assure you. Whatever you give, we will give an account of every single penny."
An American Navy ship with helicopters and 1,000 marines reached Pakistan's southern coast to boost relief efforts.