Hundreds of trucks crossed into Afghanistan from Pakistan after the border reopened for the first time in more than a month, ending the protracted closure of one of South Asia's busiest trade routes.

Fayaz Khan, an official at the Torkham border, said Prime Minister Nawaz Sharif's order to open the border at Torkham and Chaman was received late on Monday. As a result, the border opened for business at 7am on Tuesday.

The long-stranded convoy of trucks that stretched for miles on either side began to move.

Pakistan closed the border in mid-February, following a string of militant attacks that Islamabad has blamed on militants hiding in Afghanistan.

Sources in political administration of Khyber Agency told a Radio Pakistan correspondent that only those Afghan nationals will be allowed to cross the border who possess valid travelling documents.

The United Nations welcomed Pakistan's decision to open its border crossings with Afghanistan.

“We welcome the reopening of the border crossings between Pakistan and Afghanistan,” Farhan Haq, deputy spokesman for the UN Secretary-General, said in response to a question from a Pakistani journalist at the regular noon briefing.

“We hope that the people of the two countries would be able to move freely between the two countries,” he added.

The government on Monday reopened border crossings with Afghanistan as a goodwill gesture, but with a hope that Kabul would address its concerns about terrorist sanctuaries on the border.

The closure of the formal crossing points on the 2,600km porous border was ordered by the army immediately after the Sehwan shrine bombing last month. The crossings have remained closed all along except for a two-day relaxation earlier this month for the repatriation of stranded passengers, which benefited about 55,000 people.

The border closure shut down all trade between the two countries, because of which traders on both sides suffered huge losses, but landlocked Afghans bore the brunt. Price hike in Afghanistan caused by the closure badly impacted the ordinary Afghans, resulting in a surge in the already very high anti-Pakistan sentiment.

The situation was feared to escalate into a humanitarian crisis. Economic losses due to the closure, moreover, ran into millions of dollars and Kabul had taken up the matter with the World Trade Organisation, which was scheduled to take it up in the first week of April.

The closure that continued during the recently held Economic Cooperation Organisation summit in Islamabad, which was attended by Afghanistan at a lower level, sharply contrasted with its outcome document in which leaders from 10 regional countries pledged promotion of trade and connectivity linkages.

Sanctuaries of the banned Tehreek-i-Taliban Pakistan’s (TTP) and its splinter groups have existed along the border since 2010 when militants fleeing military operations in Swat and Bajaur took refuge there.

The Jamaatul Ahrar, which split with the TTP in 2014, moved its bases to Afghanistan after the start of operation Zarb-i-Azb. Several attacks have been carried out in Pakistan from those bases, but the Afghan government has always turned a blind eye to them.

Lately, it suggested it could take action against them as a quid pro quo for action against the Afghan Taliban and Haqqani network allegedly based in Pakistan.