SHIKARPUR, Pakistan — Victims of Pakistan’s deadly floods mobbed relief trucks carrying food Tuesday, and authorities in the northwest warned of famine unless the region’s farmers got immediate help with planting new crops.

The floods began three weeks ago, but there is little sign that conditions are improving for some 20 million people – or one in nine Pakistanis – who are affected. Tens of thousands of villages remain under water, and officials feared that more flooding could be on the way.

The already unpopular government has been sorely tested by the disaster, which is complicating the U.S.-backed campaign against Islamist militants. The international community is rushing water, medicine, shelter and aid workers to the country, but aid groups and the British government have complained that the response has been too slow and not generous enough.

President Asif Ali Zardari’s reputation sank to new lows after he chose to travel to Europe on a state visit as the crisis unfolded. Meeting with local aid groups, Zardari acknowledged Tuesday that the disaster response had not been very good.

“We have to move forward despite whatever criticism we get,” he added.

The U.N. asked last week for $459 million for immediate relief efforts and has received 40 percent of that so far, said spokesman Maurizio Giuliano. Another $43 million has been pledged.

“We would like our pledges to turn into checks as soon as possible because the situation is getting very bad,” Giuliano said.

The World Bank said it will redirect $900 million of its existing loans to Pakistan for use in flood recovery.

For now, people displaced by high water are living in makeshift camps alongside their livestock or in flooded towns.

“The vast geographical extent of the floods and affected populations meant that many people have yet to be reached with the assistance they desperately need,” the U.N. said. It also said the number of children and breast-feeding mothers affected and rising diarrhea cases “point toward a clear risk of malnutrition among the affected population.”

The floods have killed about 1,500 people and inundated 1.7 million acres of wheat, sugar cane and rice. Food prices have risen sharply.