The US has started using the land route through Pakistan to pull American military equipment out of Afghanistan as it draws down its troops in the country, US and Pakistani officials said on Monday.

The US moved 50 shipping containers into Pakistan over the weekend, said Marcus Spade, a spokesman for US forces in Afghanistan. The containers were the first convoys to cross into Pakistan as part of the Afghan pullout, he said.

Pakistan will be a key route for the US to withdraw tens of thousands of containers of equipment out of landlocked Afghanistan as it pulls most of its combat troops out by the end of 2014.

Pakistan closed the route for nearly seven months after US air strikes killed 24 Pakistani troops at a post along the Afghan border in November 2011. Islamabad reopened the route in July 2012 after Washington apologised for the deaths.

During the closure of the Pakistan route, the US had to use a longer, more costly path that runs north out of Afghanistan through Central Asia and Russia. The US has also used that route to withdraw equipment.

It’s unclear what took the US so long to begin withdrawing equipment through the Pakistan route, which runs south out of Afghanistan to Karachi. Supplies have been flowing into Afghanistan since the route reopened in July 2012.

Twenty-five containers that originated from a base in Kandahar entered Pakistan through the Chaman border crossing on Saturday, said Ata Mohammed, a shipping official.

Another 25 containers entered Pakistan on Sunday through the other major Afghan border crossing at Torkham in Khyber tribal area, said Mohammed Yousuf, a local political official.

The US still has about 66,000 troops in Afghanistan, down from a high of over 100,000. As it pulls out of the country, the US will have to move an estimated 50,000 vehicles, as well as about 100,000 metal containers — each about 20 feet long.

There are also about 40,000 troops from other Nato countries in Afghanistan that will have to withdraw supplies and equipment as wellAnother American military officer in Afghanistan, Lt-Col Les Carroll, told AFP the two convoys had been sent through Pakistan as a “test” as the military decides how best to withdraw the huge amount of US and Nato equipment in Afghanistan, more than 11 years after a US-led invasion brought down the Taliban.

“There are still 100,000 men and 200 bases. Some of the equipment will stay (in Afghanistan), some of it will be redeployed,” Col Carroll said.We have got to use any feasible way to do that. The northern route and of course air are other solutions.”Pakistani-US relations have now largely recovered and the outgoing US commander in Afghanistan, Gen John Allen, and his successor, Gen Joseph Dunford, on Thursday held talks with Pakistani army chief, Gen Ashfaq Parvez Kayani.

Although Pakistan is the most efficient and cheapest route, the blockade and Pakistan’s past demands for more money have made western officials wary of over reliance on Islamabad.A report in The New York Times last month said officials in Uzbekistan had offered to provide a land route for equipment leaving northern Afghanistan if vehicles and military supplies could be left behind for them.

A customs official in Jamrud said that Sunday’s containers came from Bagram, the largest US-run air base in Afghanistan, and were trucked into Pakistan under tight security provided by paramilitary troops.Hanif Khan Marwat, the president of All Pakistan Goods Carriers Association, said the convoys were on their way to Karachi port“The containers are carrying military equipmentThis is the first time that such a big number of trucks are coming back to Karachi with Nato equipment,” he said.