The US Army faces a logistics nightmare in the repatriation of military equipment worth more than $30 billion from Afghanistan, a senior official said Tuesday.

"I can always wish that Afghanistan was a coastline country and had a great port and that would be very easy but... it's not," the official told a press conference.

"Afghanistan is not Iraq (from which the US military withdrew in December). It does not have the same structures, the same access to sea ports."

But he said the US is exploring several other "multimodal solutions", including transporting the equipment by plane to a big port.

"It's much more cost effective than flying things all the way back to the US or to Europe."

The US official, who requested anonymity, said several dozen vehicles worth more than $30 billion needed to be repatriated.

"We can't wait (until) the summer of 2014 to be successful in getting everything out of here. We have to start now."

The NATO-led alliance, which has had forces in Afghanistan since a US-led invasion toppled the Taliban from power in 2001, started to withdraw its combat troops last year, with final retreat scheduled for 2014.

The withdrawal has been further complicated by strained ties with Pakistan over a deadly NATO air strike that killed 24 Pakistani soldiers in November.

"We are exploring ground options. We will continue to work with Pakistanis, to see if we can improve relations," said the official.

Senior Pakistani military and government officials say they are reviewing future cooperation with the US as relations flounder between the shaky allies in the wake of the November strike.

NATO said Monday it wants to get relations with Pakistan back on track "as quickly as possible" to reopen its key supply route for foreign troops fighting in Afghanistan.

An official at Pakistan's southern port of Karachi earlier said that NATO military vehicles and supplies were piling up at the docks, with truck drivers unable to drive them to the northwestern border to cross into Afghanistan.

Afghanistan's Taliban-led insurgency has intensified in recent years, with an increase in incidents of roadside bomb attacks and suicide explosions.

At least 12 people were killed and 28 others injured in three bomb attacks in the southern Afghan city of Kandahar on Tuesday, a police commander said.