Pakistan said it will clamp down on charities linked to militants trying to exploit anger among flood victims, amid fears their involvement in the relief effort would undermine the fight against groups like the Taliban. While Pakistan's government overwhelmed by the scale of the disaster has struggled to reach aid to millions of people, charities with much smaller resources have moved in swiftly to fill the vacuum. "The banned organisations are not allowed to visit flood-hit areas," Interior Minister Rehman Malik told Reuters. "We will arrest members of banned organisations collecting funds and will try them under the Anti-Terrorism Act." President Asif Ali Zardari and a senior U.S. senator warned on Thursday that militants were trying to promote their cause during the floods, similar to what happened after an earthquake in Pakistan Occupied Kashmir in 2005. More than 4 million Pakistanis have been made homeless by nearly three weeks of floods, making the critical task of securing greater amounts of aid more urgent. Eight million people are in urgent need of humanitarian assistance. The floods have marooned villages, destroyed power stations and destroyed roads and bridges -- lifelines for villagers -- just as the government had made some progress in stabilising the country through offensives against Taliban insurgents. The United States led a stream of pledges of more funds for Pakistan during a special meeting of the U.N. General Assembly on Thursday. U.S. Secretary of State Hillary Clinton promised a further $60 million (38 million pounds), bringing to more than $150 million (96 million pounds) the contribution Washington would make towards emergency flood relief. British Development Secretary Andrew Mitchell said London was doubling its contribution to nearly $100 million (64 million pounds). Speaking for the European Union, Belgian Foreign Minister Steven Vanackere promised a further 30 million euros ($38.5 million) on top of 110 million euros already committed. The United Nations has issued an appeal for $459 million (295 million pounds), of which Secretary-General Ban Ki-moon said about 60 percent had been pledged. U.S. Senator John Kerry, who visited flood-hit areas with President Zardari on Thursday , said action must be taken to prevent anyone from exploiting frustrations. "We need to address that rapidly to avoid their (Pakistani's) impatience boiling over, and people exploiting that impatience and I think it's important for all of us to understand that challenge," Kerry said, in a clear reference to the Taliban. "We also share security concerns." About one-third of Pakistan has been hit by the floods, with waters stretching tens of miles (km) from rivers. The United States needs a stable Pakistan, which it sees as the most important ally in the war against militancy, especially in neighbouring Afghanistan, where a Taliban insurgency is raging. In a sign of growing concerns over the ramifications of the floods, Kerry said $200 million (128 million pounds) from the $7.5 billion (4.8 billion pounds) U.S. aid package for Pakistan over five years, which he co-authored, would be diverted to the relief effort. Zardari, who drew a hail of criticism after he left on a trip to meet the leaders of Britain and France as the disaster unfolded, also said militants could capitalise on the floods.