Afghan authorities deployed hundreds of commandos and pro-government militiamen on Tuesday to counter the Taliban's blistering offensive in the north, a day after more than 1,000 government troops fled into neighbouring Tajikistan.

Fighting has raged across several provinces, but the insurgents have primarily focused on a devastating campaign across the northern countryside, seizing dozens of districts in the past two months.

Last week, all US and NATO forces left Bagram Air Base near Kabul -- the command centre for anti-Taliban operations -- effectively wrapping up their exit after 20 years of military involvement that began in the wake of the September 11 attacks

"We are planning to launch a big offensive to retake the lost territories from the enemy," Fawad Aman, a spokesman for the Ministry of Defence told AFP.

"Our forces are being organised on the ground for this operation."

Troops and pro-government militiamen were deployed in the northern provinces of Takhar and Badakshan where the Taliban have captured swathes of territory at lighting speed, often without any fighting.

Afghan defence officials have said they intend to focus on securing major cities, roads and border towns in the face of the Taliban onslaught, launched as US and NATO troops pressed ahead with their final withdrawal in early May.

The militants' successes have spurred fears that Afghan forces are in crisis, particularly now vital US air support has been massively curtailed by the handover of Bagram Air Base.

- Afghan forces flee-

On Monday, more than 1,000 Afghan troops fled into Tajikistan, forcing the neighbouring country to bolster the frontier with its own soldiers.

Several hundred had already crossed into the country in recent weeks, in the face of a Taliban offensive.

Tajik President Emomali Rakhmon has ordered "the mobilisation of 20,000 reserve troops to further strengthen the border between Tajikistan and Afghanistan," a statement from the presidency said late on Monday.

"We had to abandon our base because there was no coordination or interest among our commanders to counter the attack," said Mohammad Musa, a soldier who had fled to Tajikistan after his base in Kunduz province fell to the Taliban last week.

The fighting in the north has also forced Moscow to close its consulate in the city of Mazar-i-Sharif, the capital of Balkh province and one of Afghanistan's largest urban centres near the border with Uzbekistan.

"The situation is changing rapidly. The Afghan forces, as they say, have abandoned too many districts. This logically creates nervousness," Moscow's envoy to Afghanistan Zamir Kabulov told the state-run TASS news agency on Monday.

- 'Trying our best' -

The insurgents on Tuesday claimed to have captured a district in Nimroz province in the southwest.

The speed and ease of the Taliban's effective takeover of swathes of areas in Takhar, Badakhshan and Kunduz represent a massive psychological blow to the Afghan government.

The area once served as the stronghold for the anti-Taliban Northern Alliance during the gruesome civil war in the 1990s and was never routed by the militants.

A psychological war has also been taking shape online.

The Taliban has marshalled its forces on social media, with insurgent-affiliated accounts providing live updates of the fall of districts and posting numerous videos of Afghan soldiers surrendering and handing over huge weapons caches and equipment to the group.

The Afghan government in turn has been releasing its own footage on social media -- mostly grainy black and white videos of airstrikes obliterating alleged Taliban positions, while boasting of inflicting heavy casualties on the jihadist group.

Afghan commander General Mirassadullah Kohistani, who is now in charge of Bagram Air Base -- from where American warplanes bombed the Taliban hideouts for 20 years -- put on a brave front when asked about the insurgents rapid gains.

"We are trying to do the best and as much as possible secure and serve all the people," he said.