Afghan President Hamid Karzai on Tuesday said he wanted "at least $2 billion" a year from the United States after it withdraws its troops in 2014.

Karzai said the US should specify in a partnership agreement to be signed between his country and the US how much money it will give to Afghanistan after they leave.

"They (US) say we will give you money, but will not specify the amount. We say give us less, but write it down," Karzai told a group of university professors and students in Kabul.

"We want them to write down that America will give for Afghanistan's security $2 billion a year -- or at least two billion a year", he said. "If they want to give us more, they are welcome."

Karzai's comments came a day after he laid most of the blame for an 18-hour assault by squads of Taliban insurgents in Kabul Sunday on intelligence failures by NATO forces.

"The terrorists' infiltration in Kabul and other provinces is an intelligence failure for us and especially for NATO and should be seriously investigated," Karzai said in a statement.

The 130,000-strong US-led NATO force helping the Afghan government fight a decade-long Taliban insurgency is due to end combat operations and pull out by the end of 2014 and the two countries are in talks about their future relations.

Kabul has already achieved two preconditions for signing the treaty -- full control over the US-run Bagram prison and controversial special forces night raids against Taliban insurgents.

Officials on both sides have expressed hope that a strategic partnership agreement governing post-2014 ties could be signed ahead of a NATO summit in Chicago in May.

"We don't want them to spend a lot of money here, we would like to help them save their money, but give some to us too," Karzai said.

The US led an invasion of Afghanistan to topple the hardline Islamist Taliban regime for harbouring Al-Qaeda leader Osama bin Laden after the September 11 2001 attacks on New York and Washington.

Since then it has led a NATO fight in support of Karzai's government against a Taliban insurgency, in which nearly US 2,000 troops have died, according to monitoring group icasualties.org.