It points, among other examples, to the impounding by Israeli customs of 1,000 AK-47 rifles despite prior approval of their import by the Israeli government. It also says that US law enforcement authorities were forced to put into storage 1,400 radios for the Palestinian security forces – whose entry had also previously been approved – at a cost of $176,000 (£114,000) to the American taxpayer.

The report points to a range of evidence that the security forces have markedly improved their efficiency. But it discloses that Israel has blocked a US State Department proposal to set up a specialist Palestinian counter-terrorist unit, despite Israel's repeated calls on the forces to combat militant armed factions in the occupied West Bank.

The GAO report does not mention accusations made against the Palestinian security forces in the West Bank by human rights groups that they have unlawfully detained and abused political opponents of the Authority. Parallel charges have been made against Hamas security forces in Gaza.

Although US complaints that Israel is blocking equipment destined for the Palestinian security services in the West Bank have surfaced before, the report is the first official confirmation of the State Department's frustration at the obstacles sometimes mounted by Israel. The report's basic purpose is to establish whether the US is getting value for the $392m it has spent on training and rehabilitating the West Bank security forces since 2007. It was compiled after extensive enquiries with US, Israeli and Palestinian officials between July 2009 and May 2010.

The report acknowledges that equipment shipments are frequently approved by Israel, though there can be delays of up to a year. It also complains that the Palestinian Authority has on occasion failed to follow the precise shipment instructions contained in official authorisations for equipment imports. And it hints that US officials are chafing at State Department regulations which prevent them travelling without armed escort in the West Bank, in contrast to officials of other Western countries.

But the GAO's main concerns appear to be with obstacles mounted by Israel both at ports of entry and at checkpoints in the West Bank. It also complains that security installations can only normally be established in Area A, the only sector under supposedly direct Palestinian control, and accounting for a mere 20 per cent of the West Bank territory.

The GAO was told by US officials that Israel's insistence on considering each shipment on a "case by case" basis also affects "non-lethal" equipment. In one case, the officials said, Israel approved the shipment of raincoats to the Palestinian forces, but would not "guarantee the approval of future shipments of raincoats of comparable types and quantities".