The Taliban have taken control and raised their flag above a key border crossing between Afghanistan and Pakistan.
Social media footage showed a white flag fluttering above the Spin Boldak crossing near Kandahar. However, the Afghan government officials have denied the post has fallen.
The Taliban reportedly seized the border crossing without resistance.
In recent weeks, the militants have made rapid advances across the country, seizing a series of border posts from Afghan forces, including crossings with Iran, Tajikistan and Turkmenistan.
It comes as the United States withdraws its forces from Afghanistan ahead of an 11 September deadline set by President Joe Biden.
The Taliban have also seized control of a number of key roads as they seek to cut off supply routes to major cities.
The border post, which divides the Afghan town of Spin Boldak in Kandahar province on one side and the Pakistani town of Chaman on the other, is the second busiest crossing between the countries. It links the city of Kandahar to Pakistan’s ports, and sees some 900 trucks pass through each day.
If the Taliban are able to hold the crossing it would give them significant customs revenue from the trade which flows back and forth and would provide direct access to areas in Pakistan.
Afghan President Ashraf Ghani had promised civilians on Tuesday that “the Taliban’s backbone will be broken”, and the lost territory would be won back.
But his forces have been struggling to halt the Taliban’s advance through the country, which has sped up since a 2020 deal struck with former US President Donald Trump’s administration.
Under the terms of that deal, the US and its Nato allies agreed to withdraw all troops in return for a commitment by the militants not to allow any extremist group to operate in the areas they control.
But the Taliban did not agree to stop fighting Afghan forces. The militants are now in talks with the Afghan government, but there is no sign of stopping their attacks, with talks barely progressing.