The Taliban on Thursday seized another key border crossing in Afghanistan, this time with Iran, an Afghan official said.
The militants have been surging as American troops complete their withdrawal from Afghanistan.
In the past week, the insurgents have also taken two other crossings, on the borders with Tajikistan and Uzbekistan.
Meanwhile, President Joe Biden said the US military mission in Afghanistan would conclude on August 31.
The Taliban’s success has caused some countries to close their consulates in the region, while Tajikistan has called up reservists to reinforce its southern border with Afghanistan.
Afghan soldiers in Islam Qala, a major transit route between Afghanistan and Iran, fled from their posts, crossing into Iran for refuge, Iranian media reported.
The crossing is about 120 kilometres west of the city of Herat, the provincial capital.
Taliban spokesman Zabihullah Mujahid tweeted to confirm the taking of Islam Qala, and said fighters entered Islam Qala town and were greeted warmly by the local residents.
Mr Mujahid also posted a video purporting to show Taliban riding in the backs of lorries in the town, shooting into the air in celebration as a crowd of men cheered them on.
Afghanistan has had a Taliban surge as the American and Nato pull-out increased over the past few months.
On Tuesday, the US Central Command said 90 per cent of US troops and equipment had been withdrawn from Afghanistan.
On Sunday, the Taliban seized control of several districts from fleeing Afghan forces, several hundred of whom fled across the border into Tajikistan.
Since mid-April, when Mr Biden announced the end to Afghanistan’s “forever war”, the Taliban have made strides throughout the country.
On Thursday, Mr Biden said he did not trust the Taliban but did trust the ability of the Afghan military to defend the government.
He urged the Afghan government to reach a peace deal with the insurgents.
The Taliban’s most significant gains have been in the north, a traditional stronghold of the US-allied warlords who helped to defeat the militants in 2001.
In Badakhshan province, many districts fell without a fight.
The consulates of Turkey and Russia have reportedly closed in Mazar-e-Sharif, the capital of northern Balkh province and Afghanistan’s fourth-largest city.
The Taliban now control about a third of all 421 districts and district centres in Afghanistan. Their victories are putting pressure on provincial cities and taking away government control of key transport routes.
Islam Qala made headlines in February, when a huge fire erupted after the explosion of a fuel tanker.
At least 20 people were injured and hundreds of lorries carrying natural gas and fuel, which were lined up at the crossing, were engulfed in the blaze.
It took firefighters from both countries three days to put the blaze out. There was no suggestion of Taliban involvement in the explosion.