He was addressing the nation during much muted celebrations of Pakistan's independence from the UK 63 years ago.

The United Nations has confirmed at least one case of cholera among the victims in the Swat valley.

Health workers have been stepping up their battle against waterborne diseases in the flood-hit country.

In his address, Mr Gilani said 20 million were now homeless, although it was unclear how many of those people were temporarily forced to leave their homes and how many had lost their houses altogether.

"Unfortunately, the recent unprecedented torrential rains and devastating floods have made more than 20 million people homeless, destroyed standing crops and food worth billions of dollars and washed away bridges, roads, communication and energy networks," he said.

There were still flood victims to be reached, but the government was leaving no stone unturned, he said.

The UN had previously said the region's worst flooding in 80 years had affected 14 million out of Pakistan's 180 million population and killed 1,600 people.

UN Secretary General Ban Ki-moon is expected to visit the country over the weekend.