Moving supplies to NATO troops in Afghanistan via Central Asia costs three times as much as routes through Pakistan, which Islamabad shut seven months ago in anger, a senior US officer said Wednesday.

"On the ground, it's almost three times more expensive to come from the north as it does from Pakistan. More expensive and slower," said Vice Admiral Mark Harnitchek, director of the Defense Logistics Agency.

NATO now uses an alternative network of northern routes that pass through Russia, Central Asia and the Caucasus.

Transporting a container from the United States to Afghanistan costs about $20,000, he told a group of defense reporters.

But the cost of ferrying cargo to the Pakistani port of Karachi and then over roads to the Afghan border amounts to only a third of that price, he said.

Pakistan imposed a blockade on NATO supply convoys after 24 of its soldiers were killed by mistake in a US air strike in November along the Afghan border.

US Defense Secretary Leon Panetta said earlier this month that the Pakistan border closure costs the United States an additional $100 million a month.

Before the route cut-off, about 30-40 percent of the fuel used by coalition forces came through Pakistan.

Fuel is now transported over land via the northern routes, while food is flown in on cargo aircraft, he said.

"It was challenging initially and we took a bit of a dip there in terms of days of supply. But now our stocks of food and fuel have never been higher," Harnitchek said.

The supply routes will be on the agenda when the commander of NATO-led forces in Afghanistan, General John Allen, meets his counterparts in Pakistan on Wednesday, officials said.

US officials raised expectations in May that a deal was imminent with Pakistan on the reopening of the routes, but no announcement came and Washington withdrew its team of negotiators.

The United States has refused to issue a formal apology over the air strikes, despite appeals from Pakistan.

Amid continued deadlock, the Pentagon on Wednesday expressed hope that a deal eventually could be reached on the supply routes.

"I think there is reason for optimism. I think we're reaching a point in our relationship with Pakistan that suggests that things are settling down a bit," spokesman George Little told reporters at a Pentagon briefing.

"I think the basis for some kind of agreement on the GLOCs (ground lines of communication) is there and is real and we hope that we reach a resolution," he said.