Tajikistan has allowed the transit of NATO non-military cargo to Afghanistan by land, a US military commander said on Friday, and neighbor Kyrgyzstan formalized the closure of a US air base.

US is seeking to diversify supply routes for its troops in Afghanistan as militants in Pakistan step up attacks on supply convoys.

"Tajikistan has allowed (NATO) to use its railways and roads to transit non-military goods to Afghanistan," said Rear Admiral Mark Harnitchek of the US Transportation Command.