Floodwaters spread into Pakistan's heartland Tuesday, submerging dozens of villages along bloated rivers whose torrents already have killed at least 1,200 people.

Fresh rains in the hardest-hit northwest threatened to overwhelm a major dam and unleash a new deluge.

Relief work for some 2 million people has been delayed by swamped roads, washed out bridges and downed communication lines, and survivors have complained about government inaction. Other countries, including the U.S., have pledged assistance to Pakistan, which is already struggling to control a violent Taliban militant movement.

About 3,000 people were marooned in the Kot Addu area of southern Punjab province after the water breached a protection bank, forcing the army to stage an evacuation using boats and helicopters, said Maj. Farooq Feroz, a military spokesman.

In the northwest, new downpours Tuesday added to the misery of the worst flooding in generations.

Rising water levels at Warsak Dam, the country's third biggest, prompted disaster officials to ask residents in the northern outskirts of Peshawar city to leave their homes.

The Pakistani army, which has the helicopters, boats and infrastructure needed for relief work, is delivering food, medicine and tents, as are government agencies and several different political parties and welfare organizations.