Pakistani authorities began evacuating more than 500,000 people from flood-risk areas in the south Thursday, as the overall number of people affected by devastating floodwaters topped four million.
The floods have already ravaged the northwest, killing more than 1,500 people in the past week, washing away roads, bridges and homes, and destroying crops and farmland. Many areas are accessible only by boat and helicopter.
As monsoon rains continued Thursday, flooding spread toward Punjab and Sind provinces, where emergency search-and-rescue missions and relief operations are under way.
The World Food Program says it launched a major airlift Thursday to bring desperately needed food to tens of thousands of people cut off from the rest of the country by floodwaters.
The Pentagon says the U.S. military can divert troops from neighboring Afghanistan to help with Pakistan flood relief, in case the Islamabad government asks for more help.
Pentagon spokesman Geoff Morrell said U.S. helicopters flew 18 missions Thursday, delivering 30 tons of relief supplies and evacuating 800 people from Kalam in northwestern Khyber-Pakhtunkhwa province. The six helicopters came from Afghanistan.
The U.S. embassy in Islamabad said Washington has pledged an additional $25 million in aid to Pakistan, bringing total assistance to $35 million. The money will be given to local and international groups to provide food, water and shelter to flood victims.
The Pakistani government has been criticized for not responding fast enough to the disaster.
But the head of Pakistan's National Disaster Management Authority, Nadeem Ahmad defended the government's relief efforts, saying the scope of the disaster was beyond expectations and poor weather initially hampered rescue efforts.
Also Thursday, officials said at least 20 people died when a bus plunged into a rain-swollen river in Pakistani-controlled Kashmir.
Some information for this report was provided by AP and AFP.