SUKKUR, Pakistan – Authorities evacuated thousands of Pakistanis living along expanding rivers on Saturday as forecasts predicted even more heavy rain could deepen the country’s flood crisis. As the prime minister appealed for national solidarity, hardline Islamists rushed to fill in the gaps in the government’s aid effort.

Pakistani officials estimate as many as 13 million people throughout the South Asian nation have been affected by the worst flooding in the country’s 63-year history, though the United Nations, apparently using different metrics, has put the number at roughly 4 million. About 1,500 people have died, most of them in the northwest, the hardest-hit region.

The intense deluge that began about two weeks ago has washed away roads, bridges and many communications lines, hampering rescue efforts staged by aid organizations and the government. Incessant monsoon rains have grounded many helicopters trying to rescue people and ferry aid, including six choppers manned by U.S. troops on loan from Afghanistan.

Confidence in the national government’s ability to cope has been shaken by the decision of President Asif Ali Zardari to visit France and England amid the crisis.

Floodwaters receded somewhat Friday in the northwest, but downpours in the evening and early Saturday again swelled rivers and streams. Pakistani meteorologist Farooq Dar said heavy rains in Afghanistan were expected to make things even worse into Sunday as the bloated Kabul River surged into Pakistan’s northwest.

That will likely mean more woes for Punjab and Sindh provinces as well, as new river torrents flow east and south.

An Associated Press reporter saw many people walking on foot and using trucks to migrate to safer places in interior Sindh, where tens of thousands have fled for safer land and floodwaters have swallowed many villages. Some Pakistanis, however, refused to leave their crops and homes. Many feared that if they left and the floods never came, their household items would be stolen.

Pakistan’s military said Saturday it had rescued more than 100,000 people from flood-affected areas, while 568 army boats and 31 helicopters were being used for the rescue operation.

The army was also providing food and tents to the survivors.