MIR ALI, Pakistan — The Taliban hinted they may launch attacks against foreigners helping Pakistan respond to the worst floods in the country's history, saying their presence was "unacceptable." The U.N. said it would not be deterred by violent threats.

The militant group has attacked aid workers in the country before, and an outbreak of violence could complicate a relief effort that has already struggled to reach the 8 million people who are in need of emergency assistance.

Pakistani Taliban spokesman Azam Tariq claimed Thursday that the U.S. and other countries that have pledged support are not really focused on providing aid to flood victims but had other motives he did not specify.

"Behind the scenes they have certain intentions, but on the face they are talking of relief and help," Tariq told The Associated Press by telephone from an undisclosed location. "No relief is reaching the affected people, and when the victims are not receiving help, then this horde of foreigners is not acceptable to us at all."

He strongly hinted that the militants could resort to violence, saying "when we say something is unacceptable to us, one can draw one's own conclusion."

U.N. humanitarian chief John Holmes said the U.N. remained committed to helping flood victims in Pakistan.

"We will obviously take these threats seriously as we did before, and take appropriate precautions, but we will not be deterred from doing what we believe we need to do, which is help the people of Pakistan ... who have been affected by the flood," he told a news conference at U.N. headquarters in New York.

Holmes noted that the Pakistani Taliban carried out a suicide attack against the office of the U.N.'s World Food Program in Islamabad last October, killing five staffers, and in March, militants attacked the offices of World Vision, a U.S.-based Christian aid group helping earthquake survivors in northwestern Pakistan, killing six Pakistani employees.

He said U.N. security experts will be working with U.N. agencies and international organizations "to assess what the risks are and to minimize them."

U.S. State Department spokesman P.J. Crowley said Washington is also taking the threat of attacks by militants seriously.

"We have information of the potential targeting of foreign relief workers in Pakistan, as well as government ministries," Crowley told reporters in Washington, adding, "It just underscores the bankrupt vision that these extremists have and we are conscious of that threat."

According to the United Nations, almost 17.2 million people have been significantly affected by the floods and about 1.2 million homes have been destroyed or badly damaged.

Holmes said U.N. agencies have reached almost 2 million Pakistanis with emergency food supplies and an estimated 2.5 million with clean drinking water. He said medical treatment has been provided to about 3 million people and more than 115,000 tents and 77,000 tarpaulins have been distributed.

About 70 per cent of the $460 million initially sought by the U.N. and its humanitarian partners for flood relief -- some $325 million -- has either been contributed or pledged so far by foreign donors, while an additional $600 million has been provided or promised outside the appeal, he said.

"We're approaching $1 billion with funds offered or already contributed inside and outside the appeal for this crisis," Holmes said. "That's a reasonable response, but we certainly need more."

The floods began almost a month ago with the onset of the monsoon and have ravaged a massive swath of Pakistan, from the mountainous north to its agricultural heartland.

The U.S. military has also stepped in to help, flying helicopters that have evacuated flood victims and delivered relief supplies in Khyber Pakhtunkhwa, the northwest province that was hit hardest by the floods.

It is unclear how many foreigners are operating on the ground in Khyber Pakhtunkhwa, which borders Pakistan's semiautonomous tribal area where the Pakistani Taliban are strongest. Many aid organizations involved in the relief effort have been in Pakistan for years and use networks of locals in the most dangerous areas.

The United Nations said Thursday that the group won't let violent threats deter its relief effort.

"There is a lot of work ahead and millions of people who need our assistance," said Maurizio Giulano, spokesman for the U.N.'s Office for the Coordination of Humanitarian Affairs which Holmes heads. "We would find it inhumane for someone to target us and our work, effectively harming the millions of people whose lives we strive to save."

The Pakistani Taliban carried out a suicide attack against the office of the U.N.'s World Food Program in Islamabad last October, killing five staffers. In March, militants armed with assault rifles and a homemade bomb attacked the offices of a U.S.-based Christian aid group helping earthquake survivors in northwestern Pakistan, killing six Pakistani employees.

Violence has been relatively low in the country since the floods hit, but three bomb attacks in northwestern Pakistan on Monday killed at least 36 people.

While increased Taliban attacks would complicate the flood relief effort, the group could also risk backlash from the millions of victims who have lost everything and are desperate to receive food and shelter.

The death toll in the floods stands around 1,500 people, but the disaster ranks as one of Pakistan's worst ever because of the scale and massive economic damage, especially to the country's vital agricultural sector. The U.N. said earlier this week that some 800,000 people are still cut off by the floods and accessible only by air.

Pakistani officials urged anyone left in three southern towns Thursday to evacuate immediately as floodwaters broke through a levee, endangering areas previously untouched by the country's almost monthlong disaster.

The swollen Indus River broke through the Sur Jani embankment in southern Sindh province late Wednesday, threatening the towns of Sujawal, Daro and Mir Pur Batoro, said Mansoor Sheikh, a top government official in Thatta district.

Most of the 400,000 people who live in the area are thought to have evacuated already, but those remaining were warned to flee, he said.

Pakistan's senior meteorologist, Arif Mahmood, said high tides were preventing the Indus River from fully shedding excess water into the Arabian Sea.

"We hope these tides would fully subside after 48 hours," he said.