Pakistan's Prime Minister Yousuf Raza Gilani on Friday cancelled a visit to the United States to address the UN General Assembly because of widespread new floods, his office said.

Heavy rains in the fertile southern province of Sindh have caused flooding that has so far killed 289 people and forced 400,000 others to leave their homes, one year after the country suffered its worst-ever floods.

The prime minister has "called off his visit to New York to address United Nation General Assembly due to epidemic situation because of heavy rains and floods in Sindh province", a statement issued in English by his office said.

The statement said Gilani had instructed Foreign Minister Hina Rabbani Khar to attend the UN session on his behalf while he would visit flood-affected areas in the south from Saturday where mass relief efforts are ongoing.

The government was last year pilloried by flood victims who accused civilian authorities of a delayed and inadequate response to the disaster, which was met with nearly one billion dollars in foreign donations.

President Asif Ali Zardari met with ridicule when he failed to return home from summits in Britain and France last summer as monsoon rains triggered the floods, which affected 21 million Pakistanis.

The latest heavy rains that began falling in late August have so far affected at least 5.3 million people and deluged 1.7 million acres of arable land, government officials say.

Gilani's cancellation also comes as ties between Pakistan and the United States waver over their counterterrorism efforts along the South Asian nation's lawless northwestern border, where Taliban-linked militants hold rear bases.

The foreign ministry on Thursday said a warning by US Defense Secretary Leon Panetta, threatening unilateral US retaliation against insurgents on Pakistani soil, was "out of line" with their allied efforts.