(CNN) -- Pakistani President Asif Ali Zardari returned home Monday to face growing criticism of his actions following massive flooding in his country that has affected millions of people.
Zardari was in England for talks with British Prime Minister David Cameron during the worst of the crisis.
Ahmed Kamal, spokesman for the Pakistan Disaster Authority, said 1,203 people are confirmed dead across the country, and 1,317 have been injured. About 288,000 houses have been destroyed or seriously damaged, and more than 278,000 people have been rescued, he added.
At least 13.8 million people have been affected by the torrential rains and floods, said Maurizio Giuliano, information officer for the United Nations Office for the Coordination of Humanitarian Affairs. Giuliano said of those affected, between 6 million and 7 million are in immediate need of food and other items.
"While not all may be in need of immediate humanitarian assistance, and the severity of their needs has not yet been fully assessed, this is a higher figure than those who were affected by the 2005 South Asia tsunami (three million), the 2005 South Asia earthquake (three million), or the 2010 Haiti earthquake (three million)," he said in a statement.
Though the number of fatalities was not comparable with either the tsunami or the earthquake, both of which had death tolls that exceeded 200,000, Pakistan's flooding "is a major disaster of enormous magnitude," said United Nations Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator John Holmes.
Heavy downpours worsened conditions in Pakistan over the weekend, as aid agencies increased relief efforts to help the victims.
Many Pakistanis are not happy with the government's response to the floods, saying it has been slow and ineffective.
Prime Minister Yousaf Raza Gilani arrived in the town of Sukkur on Sunday, driving himself from the airport into town.
About a dozen families and their children -- hand-picked for the prime minister -- shook hands with Gilani. The government distributed care packages.
One woman said she was happy about the government's help. But the prime minister's convoy drove past most of the victims in Sukkur, many of whom remained angry.
The flooding, which started in the northwest, threatened places as far south as the port city of Karachi.
Peter Kessler, a spokesman for the U.N. High Commissioner for Refugees, called the situation "catastrophic."
"There are whole families just sitting and camping in the road median strips, people just lined along the streets anywhere they can get safely while there is a very real sense of nervousness that worse may be coming," Kessler said.
Districts in the southern province of Sindh were on high alert, as more rain swelled bloated rivers and inundated already-drenched earth.
Pakistan's Meteorological Department said more heavy rains were in store in the next few days, threatening to deepen the worst natural disaster the nation has experienced in recent history. And the monsoon season is only halfway over.
At least 1.4 million acres of farmland were destroyed in the province, where people rely heavily on agriculture for food.
Gilani said a true assessment of the loss of life and infrastructure can be determined only after the water recedes. He appealed to the international community and to Pakistanis living abroad to help.
As the rains continued, aid agencies scrambled to help those in need.
"The assistance that we have so far provided has alleviated suffering, but relief operations need to be massively scaled up," said Martin Mogwanja, the U.N.'s humanitarian coordinator in Pakistan.
Kessler said their warehouses were covered in more than three meters of water for days. Most of the aid in the warehouses, which are the size of Walmart supercenters, was damaged or destroyed.
He said they're hoping to salvage plastic sheeting quickly, and added that the tents are wet and need to be dried before use.
U.N. officials said the government is cooperating and granting visas and permits to get teams and aid into the country.
U.S. emergency relief teams continued to arrive in Peshawar to help, the U.S. State Department said.
The U.S. Agency for International Development has committed $35 million in aid to international organizations and nongovernmental organizations, it said.
CNN's Reza Sayah and Samson Desta contributed to this report.