Authorities in southern Pakistan say flooding in the region is getting worse as the swollen Indus river breaches more barriers and threatens to inundate towns in Sindh province.
Officials said Saturday evacuations from the historic town of Thatta have emptied it of about three-quarters of its 300,000 residents. Levees protecting the town have been breached several times in recent days, although floodwaters have not yet reached its center.
Pakistani authorities have been working to repair the barriers. Many residents of the region have taken shelter in an ancient burial ground on Makli Hill, sitting out in the open with their cattle and belongings as they wait for help.
The United Nations says flooding in the region has displaced about 1 million people since Wednesday. The floods that began one month ago in Pakistan's mountainous north before moving south have left 8 million people dependent on aid for their survival.
U.N. officials in Pakistan appealed Saturday for an intensified international response to the disaster, which has killed at least 1,600 people and affected up to 20 million.
Charities linked to Pakistan-based militant groups also have been providing assistance to flood victims.
The administrator of the U.S. Agency for International Development said the presence of suspected extremists in a flood victims' camp forced him to cut short a tour of the site Wednesday.
Speaking in Washington Friday, Rajiv Shah said he was "deeply saddened" that extremists would choose to "propagate themselves" in such environments.
Washington has said it has "credible" information that Pakistani militants may target foreign aid workers and Pakistani officials involved in flood relief efforts. U.S. officials have said they are taking the threats seriously and working with Pakistan to boost security.
Some information for this report was provided by AFP, AP and Reuters.