Holbrooke said more money was needed to stabilise the country as well as tackle Pakistan's "huge economic challenges."
"Five billion dollars is not enough for Pakistan," Holbrooke said.
"The terrorists in western Pakistan are planning other attacks around the world."
The sum of the pledges, higher than an expected $4bn, reflect the international community's concern that economic freefall in nuclear-armed Pakistan could fan popular support for al-Qaeda and other anti-government groups in the country.
"I have no doubt whatsoever that they are planning other attacks as we sit here in Tokyo and other capitals ... around the world," Holbrooke said.
"We need to work hard to strengthen the government of Pakistan, to deal with the tribal areas with all its problems.
"We should remind ourselves that the problem is far from over."
The long-term stability of Pakistan is central to a plan for South Asia by Barack Obama, the US president.
Washington is also trying to stabilise neighbouring Afghanistan, where Taliban fighters, many operating from northwest Pakistan, have stepped up their attacks against the the government.
Pakistan is also being supported by a $7.6bn loan from the International Monetary Fund (IMF) over two years.
Economists say 40 per cent of Pakistan's 160 million people live on one dollar or less a day. The government puts the figure at 33 per cent.