People wave Taliban flags after the Taliban claimed they had captured the Afghan side of the Spin Boldak border. AFP

Taliban on Wednesday said they have gained control over an important trade route linking Pakistan with southern Afghanistan, continuing sweeping gains made since foreign forces stepped up their withdrawal from Afghanistan.

The situation on the ground could not immediately be verified as no government officials were available to confirm the fall of a town in Spin Boldak district in Kandahar province situated next to the Durand Line border with Pakistan.

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Afghanistan's interior ministry denied the report even as social media was abuzz with pictures of Taliban fighters looking relaxed in the frontier town.

According to a Taliban spokesperson Zabihullah Mujahid, “The Mujahideen have captured an important border town called Wesh in Kandahar.

"With this, the important road between (Spin) Boldak and Chaman and Kandahar customs have come under Mujahideen control," he said.

Spin Boldak is the latest in a string of border crossings and dry ports seized by the Taliban in recent weeks, with the insurgents looking to choke off much-needed revenue from the government in Kabul while also filling their own coffers.

Meanwhile, Russia has urged Afghanistan and the Taliban to start meaningful negotiations on forming a transitional coalition government before it is too late, the RIA news agency cited Russia's foreign ministry as saying on Wednesday.

A Taliban delegation in Moscow last week said that the group controlled more than 85 per cent of territory in Afghanistan — an assertion dismissed by the government – and told Russia it would not let the country be used as a platform to attack others.