Another half a million or so fled had already fighting elsewhere in the north-west.
On Thursday Richard Holbrooke, the US special envoy to Afghanistan and Pakistan, met refugees at the Shah Mansoor Camp, on the outskirts of the town of Swabi.
Refugees told him about the sweltering heat and the need for adequate food.
"The size of the problem is just overwhelming. And they do not have enough international assistance by a long shot," Mr Holbrooke said.
The US says it is giving more help than the rest of the world combined
"The reconstruction phase is going to cost as much as the humanitarian phase," he added, as he renewed his call for other countries to provide more assistance to the displaced.
The United Nations has said that without the contribution of urgently-needed funds, it and its partners will only be able to feed the 2.6 million Pakistanis uprooted from Swat region for the next month or two.
Less than half of the $280m required to feed the displaced in Pakistan has come in, the UN Office for the Co-ordination of Humanitarian Affairs (OCHA) said.
Mr Holbrooke also visited the Shaikh Shahzad camp in Mardan and repeated his earlier assertion that the Taliban and not the US were the fundamental cause of suffering in the area.
He said that criticism of the US in the Pakistani media was unfair.
"There is so much false information being put out by the Taliban and al-Qaeda, and because there are so many small illegal FM radio stations... a lot of misinformation is out there."
Humanitarian focus
Correspondents say Mr Holbrooke, who arrived in Islamabad on Wednesday, wants to focus in public on the issue of helping those displaced by the fighting.
He pointed out on Wednesday that the US was providing the bulk of all the assistance to Pakistan's refugees.
The BBC's Chris Morris in Islamabad says concentrating on the humanitarian crisis is a deliberate strategy in a country where the United States is not popular.
Mr Holbrooke is as ever treading a diplomatic tightrope - wanting to express support for military action by Pakistan, without giving the impression that it is being done at the behest of the US, our correspondent says.
A new report from the International Crisis Group has warned that unless relief, rehabilitation and reconstruction efforts are urgently improved, the army's offensive against the Taliban risks leaving extremists as the ultimate winners.
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