* Areas cut off from supplies
* Zardari faces mounting anger
* Heavy damage to the economy, UN prepares aid appeal (Adds U.N. secretary-general, paragraph 13)
By Junaid Khan
MINGORA, Pakistan, Aug 9 (Reuters) - Soldiers and aid workers struggled on Monday to reach at least a million people cut off by landslides that have complicated relief efforts after the worst floods in Pakistan in 80 years.
Poor weather has grounded relief helicopters and more rain was expected to compound the misery of more than 13 million people -- about 8 percent of the population -- whose lives have been disrupted by the floods, including two million homeless.
The floods have killed more than 1,600 people.
In the Swat Valley, northwest of Islamabad, soldiers and aid workers are using mules or traveling on foot to reach people in desperate need of help.
The catastrophe has put unpopular President Asif Ali Zardari on the defensive while raising the profile of the military which is spearheading relief efforts.
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The floods, which began 10 days ago after heavy monsoon rain over the upper reaches of the Indus river basin, have ploughed a swathe of destruction more than 1,000 km (600 miles) long from northern Pakistan to the southern province of Sindh.
While the water has begun to recede in some parts of the north, water-logged mountainsides long stripped of forest cover have begun to slide in some areas, isolating communities.
"We have brought in 130 mules to take food supplies to the cut-off valleys," an army spokesman in Swat, Major Mushtaq Khan, told Reuters, adding that bad weather had grounded helicopters for the past two days.
"About one million people are stranded because the main road link has been severed ... We believe that most stocks villagers had, have been exhausted and they need supplies."
Zardari's decision to go ahead with official trips to Europe during the crisis has renewed criticism of his leadership. The military has taken the lead in relief efforts while the government is under fire for perceived dithering.
The president is expected back by mid-week.
Analysts say there is no chance the military, which has vowed to stay out of politics and is preoccupied fighting militants, will try to seize power.
ISLAMISTS FILL AID VOID
U.N. Secretary-General Ban Ki-moon said in New York on Monday that he was "extremely concerned" about the humanitarian impact of the floods in Pakistan and would soon launch an emergency aid appeal for several hundred million dollars.
The United Nations said in terms of the number of people who have lost their homes or livelihoods, and will need short- or long-term help, the floods were worse than the 2004 tsunami, which killed 236,000 people around the Indian Ocean.
In Punjab province, army helicopters rescued people and their livestock from rooftops in Mehmood Kot village, a scene being played out in many parts of the country.
Some soldiers are getting frustrated by people's reluctance to leave their homes.
"When we try to take them, they say they don't want to leave and instead they demand food. We have to fly again to bring food. This is a major problem for us," Lieutenant Colonel Salman Rafiq said.
One woman gave birth to twin boys in her flooded house in the town of Sanawa. Neighbors carried the woman and her babies on a rope bed through the flood to a helicopter.
U.S. officials are also concerned about the damage caused by the weak government response to the floods and mounting hostility toward Zardari. [nN08197550]
Pakistan is a key U.S. ally whose help Washington needs to end a nine-year insurgency by Taliban militants in Afghanistan.
Heavy rain has also hit India where military helicopters plucked about 150 foreign tourists to safety in the Himalayan region of Ladakh where flash floods have killed 156 people.
Charities with links to militants have taken advantage of the vacuum left by the Pakistani government and delivered aid to thousands, possibly boosting their standing among Pakistanis as Taliban militants press on with their war. [nSGE67805I]
U.S. concerns are also growing over the disaster's impact on Pakistan's fragile economy and how Washington's robust development plan may be slowed down to deal with the crisis.
Pakistan's economy will need huge injections of foreign aid. It turned to the International Monetary Fund in 2008 to avert a balance of payments crisis and has been struggling to meet the conditions of that $10.66 billion emergency loan.
Pakistani stocks .KSE closed 2.8 percent lower at 10,026.20, near a one-month low, as investors contemplated the extent of the flood damage, dealers said. [nSGE67806U]
In the southern province of Sindh, which has yet to see the full force of the deluge flowing south to the sea, up to one million people have been evacuated from low-lying areas. (Additional reporting by Zeeshan Haider, Kamran Haider, Adrees Latif and Faisal Aziz; Sue Pleming in Washington, Louis Charbonneau at the United Nations; Writing by Michael Georgy; Editing by Robert Birsel and Sanjeev Miglani)