Iran's foreign ministry called Friday for security guarantees  for its diplomats in Herat, after Taliban militants seized the western city in neighbouring Afghanistan.

"The Islamic republic is concerned over the escalating violence in Afghanistan, and in light of the Taliban taking control of Herat, calls for guarantees of complete safety for its diplomatic missions and the lives of its staff," foreign ministry spokesman Saeed Khatibzadeh tweeted.

He said the ministry was "in contact" with its staff in the city, which lies just 115 kilometres (70 miles) from the Iranian border.

The Taliban seized Herat on Thursday, the latest in a string of regional capitals it has wrested from government forces as US forces withdraw after a two-decade occupation.

On Friday, it also captured Kandahar, the nation's second-biggest city, leaving only Kabul and other pockets of territory in government hands.

The United States and Britain ordered the deployment Friday of thousands of troops to evacuate their nationals from the Afghan capital.

The Iranian foreign ministry's West Asia chief Rusoul Mosavi said staff at its Herat mission were "well", the official IRNA news agency reported Friday. 

Without specifying their number, he said they were still inside the mission and that "the forces that now control the city gave guarantees of full protection for the consulate, diplomats and other staff".

IRNA reported Thursday that the consulate had been closed over security fears.

Before taking Herat, the Taliban had seized Afghanistan's biggest border crossing with Iran at Islam Qala.

The Taliban, which ruled Afghanistan from 1996 until it was toppled in 2001 in a US-led invasion, has made sweeping advances since launching an offensive in May as foreign forces started withdrawing. 

The hardline Sunni Islamist movement has taken over much of the country's north, south and west.

Shiite-majority regional powerhouse Iran said Thursday it had also closed its consulate in the traditional anti-Taliban bastion of Mazar-i-Sharif over security fears.

The northern city holds bitter memories for Iranians. 

In 1998, Taliban troops entered the Iranian consulate there, killing several diplomats and an official news agency journalist.

The Taliban later said they had been killed by individuals acting independently, but Tehran held the movement responsible for the deaths, which sparked outrage and nearly triggered an Iranian military intervention in Afghanistan.

Iran Foreign Minister Mohammad Javad Zarif told Afghan channel Tolo News in December 2020 that "we have neither forgiven nor have we forgotten" the episode. 

"You may remember that our troops were stationed across the border. A war was about to erupt. The Iranian government, however, concluded that such a war would certainly harm the Afghan people, not only the Taliban. Therefore, we withdrew from waging a war and taking revenge."

Analysts say Tehran is taking a pragmatic stance on the Taliban's resurgence in Afghanistan, with which it shares a 900-kilometre border.

Major General Hossein Salami, commander of Iran's Revolutionary Guards Corps, said there was "no concern" over security of the border, adding that Iranian forces "control and monitor" the frontier, the Guards' official website Sepah News reported Friday.