UN Secretary-General Ban Ki-moon arrived in Pakistan on Sunday to visit areas devastated by the country's worst floods.
Ban was met at Islamabad's Chaklala airbase by Foreign Minister Shah Mahmood Qureshi and Interior Minister Rehman Malik.
"I will have an opportunity to see for myself the affected area and I get to share for stories and plights of affected people," Ban told reporters at the airport.
The UN has appealed for $460 million dollars to assist millions of refugees displaced by floods that have killed about 1,400 people. But international response has been slow.
Donors have pledged barely 20 percent of the funds that the UN says are required to supply food, shelter, medicine and clean water to the six million people in immediate need.
"I am here to urge the world community to step up assistance to Pakistan people," Ban said. "We are trying to mobilise all the necessary assistance, and remember that the whole world is behind the people of Pakistan at this time of trial."
About 20 million people were left homeless, according to the Pakistani government.
Floods that ravaged large parts of the north-western province of Khyber-Pakhtunkhwa and central Pakistan are submerging more areas in the southern province of Sindh, where hundreds of thousands of people are on move.
More than 700,000 houses and over 3.2 million hectares of standing crops have been destroyed or damaged, officials said.